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{{Short description|Free and open-source object relational database management system}}
{{Infobox_Software |
{{Use mdy dates|date=February 2019}}
name = PostgreSQL |
{{Infobox software
logo = [[Image:Postgresql elephant.svg|150px|PostgreSQL logo]] |
| name = PostgreSQL
developer = PostgreSQL Global Development Group |
| logo = Postgresql elephant.svg
latest_release_version = 8.2.4 |
| logo caption = ''The World's Most Advanced Open Source Relational Database''<ref>{{cite web|title=PostgreSQL|quote=PostgreSQL: The World's Most Advanced Open Source Relational Database|url=https://www.postgresql.org|access-date=2019-09-21}}</ref>
latest_release_date = [[April 23]], [[2007]] |
<!-- | screenshot = PostgreSQL 13.2 screenshot.png -->
operating_system = [[Cross-platform]] |
| developer = PostgreSQL Global Development Group<ref name="contributors" />
genre = [[ORDBMS]] |
| released = {{Start date and age|1996|07|08|br=yes|df=yes}}<ref name="birthday" />
license = [[BSD license|BSD]] |
| latest release version = {{wikidata|property|edit|reference|P548=Q2804309|P348}}
website = [http://www.postgresql.org/ www.postgresql.org] |
| latest release date = {{start date and age|{{wikidata|qualifier|P548=Q2804309|P348|P577}}}}
| latest preview version = 17 Beta 1
| latest preview date = {{Start date and age|2024|05|23|br=yes|df=yes}}<ref>{{Cite web
|url=https://www.postgresql.org/about/news/postgresql-17-beta-1-released-2865/
|title=PostgreSQL 17 Beta 1 Released!
|publisher=The PostgreSQL Global Development Group
|date=2024-05-23
|website=PostgreSQL
|access-date=2024-05-24}}</ref>
| programming language = [[C (programming language)|C]]
| genre = [[Relational database|RDBMS]]
| license = PostgreSQL License ([[free and open-source]], [[Permissive software licence|permissive]])<ref name="about/licence" /><ref name="approved by OSI" /><ref name="OSI" />
}}
{{Infobox software license
| name = PostgreSQL License<ref name="about/licence" />
| image =
| caption = PostgreSQL License
| author =
| version =
| publisher = PostgreSQL Global Development Group<br />Regents of the University of California
| date =
| OSI approved = Yes<ref name="OSI" />
| Debian approved = Yes<ref>{{Cite web|title=Debian -- Details of package postgresql in sid|url=https://packages.debian.org/unstable/postgresql|access-date=2021-01-25|website=packages.debian.org}}</ref><ref>{{cite web |url=https://fedoraproject.org/wiki/Licensing:Main?rd=Licensing |title=Licensing:Main |work=FedoraProject}}</ref>
| FSF approved = Yes<ref>{{cite web |url=https://directory.fsf.org/wiki/PostgreSQL |title=PostgreSQL |work=fsf.org}}</ref>
| GPL compatible = Yes
| copyleft = No
| linking = Yes
| website = {{URL|postgresql.org/about/licence}}
}}
}}
{{Portal|Free software}}
'''PostgreSQL''' is a [[free software]] [[object-relational database|object]]-[[relational database management system]] (ORDBMS), released under a [[BSD license|BSD-style license]]. It offers an alternative to [[List of relational database management systems|other database systems]]. Similar to other free software projects such as [[Apache HTTP Server|Apache]], [[GNU/Linux]], and [[MediaWiki]], PostgreSQL is not controlled by any single company, but relies on a global community of developers and companies to develop it.


'''PostgreSQL''' ({{IPAc-en|ˈ|p|oʊ|s|t|ɡ|ɹ|ɛ|s|_|ˌ|k|juː|_|ˈ|ɛ|l}}, {{respell|POHST|gres|_|kyoo|_|el}}),<ref>{{cite web | url=https://wiki.postgresql.org/wiki/FAQ#What_is_PostgreSQL.3F_How_is_it_pronounced.3F_What_is_Postgres.3F | title=FAQ: What is PostgreSQL? How is it pronounced? What is Postgres? | work=PostgreSQL Wiki | publisher=PostgreSQL community | access-date=October 2, 2021}}</ref><ref name="Audio sample" /> also known as '''Postgres''', is a [[free and open-source software|free and open-source]] [[relational database management system]] (RDBMS) emphasizing [[extensibility]] and [[SQL]] compliance.
PostgreSQL's unusual-looking name makes some readers pause when trying to pronounce it, especially those who pronounce [[SQL]] as "sequel". PostgreSQL's developers pronounce it {{IPA|/poːst ɡɹɛs kjuː ɛl/}}. ([http://www.postgresql.org/files/postgresql.mp3 Audio sample], 5.6k [[MP3]]). It is also common to hear it abbreviated as simply "postgres", which was its original name. The name refers to the project's origins as a "post-Ingres" database, the original authors having also developed the [[Ingres]] database.
PostgreSQL features [[transaction processing|transactions]] with [[atomicity (database systems)|atomicity]], [[consistency (database systems)|consistency]], [[isolation (database systems)|isolation]], [[durability (database systems)|durability]] ([[ACID]]) properties, automatically updatable [[view (SQL)|view]]s, [[materialized view]]s, [[database trigger|triggers]], [[foreign key]]s, and [[stored procedure]]s.<ref name="intro-whatis" />
It is supported on all major [[operating systems]], including [[Linux]], [[FreeBSD]], [[OpenBSD]], [[macOS]], and [[Microsoft Windows|Windows]], and handles a range of workloads from single machines to [[data warehouse]]s or [[web services]] with many [[concurrent user]]s.


The PostgreSQL Global Development Group focuses only on developing a [[database engine]] and closely related components.
==History==
This core is, technically, what comprises PostgreSQL itself, but there is an extensive developer community and ecosystem that provides other important feature sets that might, traditionally, be provided by a proprietary software vendor.
PostgreSQL has had a lengthy evolution, starting with the [[Ingres]] project at [[UC Berkeley]]. The project leader, [[Michael Stonebraker]], had left Berkeley to commercialize Ingres in 1982, but eventually returned to academia. After returning to Berkeley in 1985, Stonebraker started a post-Ingres project to address the problems with contemporary database systems that had become increasingly clear during the early 1980s. While they share many of the same ideas, the code bases of PostgreSQL and Ingres started (and remain) completely separated.
These include special-purpose database engine features, like those needed to support a [[Spatial database|geospatial]]<ref>
{{cite web
|url=https://postgis.net/
|title=PostGIS
|author=<!--Not stated-->
|date=2023-12-18
|website=postgis.net
|access-date=2023-12-18
|quote=PostGIS extends the capabilities of the PostgreSQL relational database by adding support for storing, indexing, and querying geospatial data.}}
</ref> or [[Temporal database|temporal]]<ref name="temporal-extensions">
{{cite web
|url=https://wiki.postgresql.org/wiki/Temporal_Extensions
|title=Temporal Extensions
|author=<!--Not stated-->
|date=2023-12-18
|website=PostgreSQL Wiki
|access-date=2023-12-18
|quote=Postgres can be extended to become a Temporal Database. Such databases track the history of database content over time, automatically retaining said history and allowing it to be altered and queried.}}
</ref> database or features which emulate other database products.<ref>
{{cite web
|url=https://github.com/orafce/orafce
|title=Orafce - Oracle's compatibility functions and packages
|author=<!--Not stated-->
|date=2023-12-17
|website=GitHub.com
|access-date=2023-12-18
|quote=Functions and operators that emulate a subset of functions and packages from the Oracle RDBMS.}}
</ref><ref>
{{cite web
|url=https://github.com/MigOpsRepos/pg_dbms_job#readme
|title=pg_dbms_job
|author=<!--Not stated-->
|date=2023-11-08
|website=GitHub.com
|access-date=2023-12-18
|quote=PostgreSQL extension to schedules and manages jobs in a job queue similar to Oracle DBMS_JOB package.}}
</ref><ref>
{{cite web
|url=https://wiltondb.com/
|title=WiltonDB
|author=<!--Not stated-->
|date=2023
|website=WiltonDB
|access-date=2023-12-18
|quote=WiltonDB [is] packaged for Windows. It strives to be usable as a drop-in replacement to Microsoft SQL Server.}}
</ref><ref>
{{cite web
|url=https://babelfishpg.org/
|title=Babelfish for PostgreSQL
|author=<!--Not stated-->
|website=babelfishpg.org
|access-date=2023-12-18
|quote=Babelfish for PostgreSQL ... provides the capability for PostgreSQL to understand queries from applications written for Microsoft SQL Server.}}
</ref>
Also available from third parties are a wide variety of user and machine interface features, such as [[graphical user interface]]s<ref>
{{cite web
|url=https://wiki.postgresql.org/wiki/PostgreSQL_Clients
|title=PostgreSQL Clients
|author=<!--Not stated-->
|date=2023-10-18
|website=wiki.postgresql.org
|access-date=2023-12-18
|quote=This page is a partial list of interactive SQL clients (GUI or otherwise) ... that you can type SQL in to and get results from them.}}
</ref><ref>
{{cite web
|url=https://wiki.postgresql.org/wiki/Design_Tools
|title=Design Tools
|author=<!--Not stated-->
|date=2023-10-23
|website=wiki.postgresql.org
|access-date=2023-12-18
|quote=Tools to help with designing a schema, via creating Entity-Relationship diagrams and similar. Most are GUI.}}
</ref><ref>
{{cite web
|url=https://wiki.postgresql.org/wiki/Community_Guide_to_PostgreSQL_GUI_Tools
|title=Community Guide to PostgreSQL GUI Tools
|author=<!--Not stated-->
|date=2023-12-01
|website=wiki.postgresql.org
|access-date=2023-12-18
|quote=This page is a list of miscellaneous utilities that work with Postgres (ex: data loaders, comparators etc.).}}
</ref> or [[Load balancing (computing)|load balancing]] and [[high availability]] toolsets.<ref>
{{cite web
|url=https://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling
|title=Replication, Clustering, and Connection Pooling
|author=<!--Not stated-->
|date=2020-07-13
|website=wiki.postgresql.org
|access-date=2023-12-18
|quote=There are many approaches available to scale PostgreSQL beyond running on a single server. ... There is no one-size fits all...}}
</ref>
The large third-party PostgreSQL support network of people, companies, products, and projects, even though not part of The PostgreSQL Development Group, are essential to the PostgreSQL database engine's adoption and use and make up the PostgreSQL ecosystem writ large.<ref>This is recognized by the liberal permission to use the PostgreSQL name, as approved (for fair use, when '''not''' confusing people about a legal relationship with the actual PostgreSQL project) when used in support of PostgreSQL, subject to the PostgreSQL Trademark Policy:
{{cite web
|url=https://www.postgresql.org/about/policies/trademarks/
|title=Trademark Policy
|author=<!--Not stated-->
|website=PostgreSQL.org
|date=2020-12-08
|access-date=2023-12-17
|quote=We will try to work with you to permit uses [of the PostgreSQL name] that support the PostgreSQL project and our Community.}}</ref>


PostgreSQL was originally named POSTGRES, referring to its origins as a successor to the [[Ingres (database)|Ingres]] database developed at the [[University of California, Berkeley]].<ref name="design" /><ref name="about/history" /> In 1996, the project was renamed <q>PostgreSQL</q> to reflect its support for [[SQL]]. After a review in 2007, the development team decided to keep the name PostgreSQL and the alias Postgres.<ref name="Project name" />
The resulting project, named '''POSTGRES''', aimed to introduce the minimum number of features needed to add complete support for types. These features included the ability to define types, but also the ability to fully describe relationships &ndash; something used widely before this time but maintained entirely by the user. In POSTGRES the database "understood" relationships, and could retrieve information in related tables in a natural way using ''rules''.


== History ==
Starting in 1986 the team released a number of papers describing the basis of the system, and by 1988 the project had a prototype version up and running. The team released version 1 to a small number of users in June 1989, followed by version 2 with a re-written rules system in June 1990. 1991's version 3 re-wrote the rules system again, but also added support for multiple storage managers and for an improved query engine. By 1993 a huge number of users existed and began to overwhelm the project with requests for support and features. After releasing a Version 4 — primarily as a cleanup — the project ended.
PostgreSQL evolved from the [[Ingres (database)|Ingres]] project at the University of California, Berkeley. In 1982, the leader of the Ingres team, [[Michael Stonebraker]], left Berkeley to make a proprietary version of Ingres.<ref name="design" /> He returned to Berkeley in 1985, and began a post-Ingres project to address the problems with contemporary database systems that had become increasingly clear during the early 1980s. He won the [[Turing Award]] in 2014 for these and other projects,<ref>{{Cite web |url=https://amturing.acm.org/award_winners/stonebraker_1172121.cfm |title=Michael Stonebraker – A.M. Turing Award Winner |quote=Techniques pioneered in Postgres were widely implemented [..] Stonebraker is the only Turing award winner to have engaged in serial entrepreneurship on anything like this scale, giving him a distinctive perspective on the academic world. |website=amturing.acm.org |language=en |access-date=March 20, 2018}}</ref> and techniques pioneered in them.


The new project, POSTGRES, aimed to add the fewest features needed to completely support [[data type]]s.<ref name="Stonebraker" /> These features included the ability to define types and to fully describe relationships{{snd}} something used widely, but maintained entirely by the user. In POSTGRES, the database understood relationships, and could retrieve information in related tables in a natural way using ''rules''. POSTGRES used many of the ideas of Ingres, but not its code.<ref name="pavel-history" />
Although the POSTGRES project had officially ended, the [[BSD license]] (under which Berkeley had released POSTGRES) enabled [[open source|open-source]] developers to obtain copies and to develop the system further. In 1994 two [[University of California, Berkeley|UC Berkeley]] graduate students, Andrew Yu and Jolly Chen, added a [[SQL]] language interpreter to replace the earlier Ingres-based [[QUEL]] system, creating Postgres95. The code was subsequently released to the web to find its own way in the world.


Starting in 1986, published papers described the basis of the system, and a prototype version was shown at the 1988 ACM [[SIGMOD]] Conference. The team released version 1 to a small number of users in June 1989, followed by version 2 with a re-written rules system in June 1990. Version 3, released in 1991, again re-wrote the rules system, and added support for multiple storage managers<ref>A Brief History of PostgreSQL [https://www.postgresql.org/docs/9.3/history.html "Version 3 appeared in 1991 and added support for multiple storage managers, an improved query executor, and a rewritten rule system."]. ''postgresql.org''. ''The PostgreSQL Global Development Group'', Retrieved on March 18, 2020.</ref> and an improved query engine. By 1993, the number of users began to overwhelm the project with requests for support and features. After releasing version 4.2<ref name="University POSTGRES" /> on June 30, 1994{{snd}} primarily a cleanup{{snd}} the project ended. Berkeley released POSTGRES under an [[MIT License]] variant, which enabled other developers to use the code for any use. At the time, POSTGRES used an Ingres-influenced [[QUEL query languages|POSTQUEL query language]] interpreter, which could be interactively used with a [[console application]] named <kbd>''monitor''</kbd>. <!-- See http://db.cs.berkeley.edu/postgres-v4r2/postgres-setup.ps -->
In July 1996, Marc Fournier at [[Hub.Org Networking Services]] provided the first non-university development server for the open source development effort. Along with Bruce Momjian and Vadim B. Mikheev, work began to stabilize the code inherited from UC Berkeley, with the first open source version released on August 1st 1996.


In 1994, Berkeley graduate students Andrew Yu and Jolly Chen replaced the POSTQUEL query language interpreter with one for the SQL query language, creating Postgres95. The <kbd>''monitor''</kbd> console was also replaced by <kbd>psql</kbd>. Yu and Chen announced the first version (0.01) to [[beta tester]]s on May 5, 1995.<!-- email lists are not citable, however see message 3165 of |url=http://db.cs.berkeley.edu/postgres-v4r2/mail-archive/1995.05.tar.gz |title=Announcement: Postgres95 Beta |author=Andrew K. Yu |date=May 1, 1995 --> Version 1.0 of Postgres95 was announced on September 5, 1995, with a more liberal license that enabled the software to be freely modifiable.<!-- message 3279 of |url=http://db.cs.berkeley.edu/postgres-v4r2/mail-archive/1995.09.tar.gz |title=ANNOUNCEMENT for postgres95 version 1.0 |author=Jolly Chen |date=September 5, 1995 -->
1996 saw a re-naming of the project: in order to reflect the database's new SQL query language, Postgres95 became '''PostgreSQL'''. The first PostgreSQL release formed version 6.0 in January 1997. Since then, a group of database developers and volunteers from around the world, coordinating via the [[Internet]], have maintained the software.


On July 8, 1996, Marc Fournier at Hub.org Networking Services provided the first non-university development server for the open-source development effort.<ref name="birthday" /> With the participation of Bruce Momjian and Vadim B. Mikheev, work began to stabilize the code inherited from Berkeley.
Although the license allowed for the commercialization of Postgres, the Postgres code did not develop commercially with the same rapidity as Ingres — somewhat surprisingly considering the advantages Postgres offered. The main offshoot originated when Paula Hawthorn (an original Ingres team member who moved from Ingres) and Michael Stonebraker formed [[Illustra Information Technologies]] to commercialize Postgres.


In 1996, the project was renamed to PostgreSQL to reflect its support for SQL. The online presence at the website PostgreSQL.org began on October 22, 1996.<ref name="20th anniversary" /> The first PostgreSQL release formed version 6.0 on January 29, 1997. Since then developers and volunteers around the world have maintained the software as The PostgreSQL Global Development Group.<ref name="contributors" />
In 2000, former Red Hat investors put together a company known as Great Bridge to commercialize PostgreSQL and compete against commercial database vendors. Great Bridge sponsored several PostgreSQL developers and donated many resources back to the community, however by late 2001 the company closed its doors citing tough competition from companies like Red Hat as well as poor market conditions.


The project continues to make releases available under its [[free and open-source software]] PostgreSQL License. Code comes from contributions from proprietary vendors, support companies, and open-source programmers.
In 2001, Command Prompt, Inc. released Mammoth PostgreSQL, the oldest surviving commercial PostgreSQL distribution. They continue to actively support the PostgreSQL community through developer sponsorships and projects including PL/Perl, PL/php, and hosting of community projects such as the [[PostgreSQL Build Farm]].


== Multiversion concurrency control (MVCC) ==
In January 2005, PostgreSQL received backing by another database vendor. [[Pervasive Software]], well known for their [[Btrieve]] product which was ubiquitous on the [[Novell NetWare]] platform, announced commercial support & community participation. While they achieved success for a time, in July 2006, Pervasive left the PostgreSQL support market.<ref name=pervasive-support>{{cite web |author=[[John Farr]] |date=2006-07-25 |title=Open letter to the PostgreSQL Community |publisher=[[Pervasive Software]] |url=http://www.pervasive-postgres.com/letter.asp |accessdate=2007-02-13 }}</ref>
PostgreSQL manages [[concurrency control|concurrency]] through [[multiversion concurrency control]] (MVCC), which gives each transaction a "snapshot" of the database, allowing changes to be made without affecting other transactions. This largely eliminates the need for read locks, and ensures the database maintains [[ACID (computer science)|ACID]] principles. PostgreSQL offers four levels of [[isolation (database systems)|transaction isolation]]: Read Uncommitted, Read Committed, Repeatable Read and Serializable. Because PostgreSQL is immune to dirty reads, requesting a Read Uncommitted transaction isolation level provides read committed instead. PostgreSQL supports full [[serializability]] via the serializable [[snapshot isolation]] (SSI) method.<ref name="ports" /> The PostreSQL MVCC implementation is prone to performance issues that require tuning when under a heavy write load which updates existing rows.<ref>{{Cite web|url=https://ottertune.com/blog/the-part-of-postgresql-we-hate-the-most|title=The part of PostgreSQL we hate the most |website= OtterTune|type= blog | author1= Bohan Zhang |author2= Andy Pavlo| date=2023}}</ref>


== Storage and replication ==
In mid-2005 two other companies announced plans to commercialize PostgreSQL with focus on separate niche markets. [[EnterpriseDB]] announced plans to focus on adding functionality to allow applications written to work with [[Oracle database|Oracle]] to be more readily run atop PostgreSQL. [[Greenplum]] contributed enhancements directed at [[data warehouse]] and [[business intelligence]] applications, notably including the BizGres project.


=== Replication ===
In October 2005, John Loiacono, executive vice-president of software at [[Sun Microsystems]], commented that "We're not going to [[Original equipment manufacturer|OEM]] Microsoft but we are looking at PostgreSQL right now,"<ref>{{cite news |author=Rodney Gedda |date=2005-10-05 |title=Sun's software chief eyes databases, groupware |publisher=[[Computerworld]] |url=http://www.computerworld.com.au/index.php/id;116679278;fp;16;fpid;0 |accessdate=2007-02-13 }}</ref> although no specifics were released at that time. By November 2005, Sun Microsystems had announced support for PostgreSQL.<ref>{{cite press release |date=2005-11-17 |title=Sun Announces Support for Postgres Database on Solaris 10 |publisher=[[Sun Microsystems]] |url=http://www.sun.com/smi/Press/sunflash/2005-11/sunflash.20051117.1.html |accessdate=2007-02-13 }}</ref> As of June 2006, Sun Solaris 10 6/06 ships PostgreSQL.
PostgreSQL includes built-in binary replication based on shipping the changes ([[Write-ahead logging|write-ahead logs]] (WAL)) to replica nodes asynchronously, with the ability to run read-only queries against these replicated nodes. This allows splitting read traffic among multiple nodes efficiently. Earlier replication software that allowed similar read scaling normally relied on adding replication triggers to the master, increasing load.


PostgreSQL includes built-in synchronous replication<ref name="H Online" /> that ensures that, for each write transaction, the master waits until at least one replica node has written the data to its transaction log. Unlike other database systems, the durability of a transaction (whether it is asynchronous or synchronous) can be specified per-database, per-user, per-session or even per-transaction. This can be useful for workloads that do not require such guarantees, and may not be wanted for all data as it slows down performance due to the requirement of the confirmation of the transaction reaching the synchronous standby.
As for the PostgreSQL project itself, it continues to make yearly major releases and minor "bugfix" releases, all available under the BSD license, based on contributions from both commercial vendors, support companies, and open source hackers at large.


Standby servers can be synchronous or asynchronous. Synchronous standby servers can be specified in the configuration which determines which servers are candidates for synchronous replication. The first in the list that is actively streaming will be used as the current synchronous server. When this fails, the system fails over to the next in line.
==Features==
===Functions===
Functions allow blocks of code to be executed by the server. Although these blocks can be written in SQL, the lack of basic programming operations, such as [[control flow|branching]] and [[iteration|looping]], has driven the adoption of other languages inside of functions. Some of the languages can even execute inside of triggers. Functions in PostgreSQL can be written in the following languages:


Synchronous [[multi-master replication]] is not included in the PostgreSQL core. Postgres-XC which is based on PostgreSQL provides scalable synchronous multi-master replication.<ref name="Postgres-XC" /> It is licensed under the same license as PostgreSQL. A related project is called [[Postgres-XL]]. Postgres-R is yet another [[Fork (software development)|fork]].<ref name=postgres-r /> Bidirectional replication (BDR) is an asynchronous multi-master replication system for PostgreSQL.<ref name=bdr />
*A built-in language called [[PL/pgSQL]] resembles Oracle's procedural language [[PL/SQL]].
*Scripting languages are supported through [[PL/Perl]], [http://www.commandprompt.com/community/plphp plPHP], [http://www.postgresql.org/docs/current/interactive/plpython.html PL/Python], [http://raa.ruby-lang.org/project/pl-ruby PL/Ruby], [http://plsh.projects.postgresql.org/ PL/sh], [http://www.postgresql.org/docs/current/interactive/pltcl.html PL/Tcl] and [http://plscheme.projects.postgresql.org/ PL/Scheme].
*Compiled languages [[C (programming language)|C]], [[C++]], or Java (via [http://pljava.projects.postgresql.org/ PL/Java]).
*The statistical language [[R programming language|R]] through [http://www.joeconway.com/plr/ PL/R].


Tools such as repmgr make managing replication clusters easier.
PostgreSQL supports row-returning functions, where the output of the function is a set of values which can be treated much like a table within queries.


Several asynchronous trigger-based replication packages are available. These remain useful even after introduction of the expanded core abilities, for situations where binary replication of a full database cluster is inappropriate:
Functions can be defined to execute with the privileges of either the caller or the user who defined the function. Functions are sometimes referred to as ''[[stored procedures]]'', although there is a slight technical distinction between the two.


* [[Slony-I]]
===Indices===
* Londiste, part of SkyTools (developed by [[Skype]])
User-defined [[Index (database)|index]] methods can be created, or the built-in [[B-tree]], [[hash table]] and [[GiST]] indices can be used. Indexes in PostgreSQL also support the following features:
* Bucardo multi-master replication (developed by [[Backcountry.com]])<ref name="Fischer" />
* [[SymmetricDS]] multi-master, multi-tier replication


=== Indexes ===
*PostgreSQL is capable of scanning indexes backwards when needed; a separate index is never needed to support <code>ORDER BY ''field'' DESC</code>.
PostgreSQL includes built-in support for regular [[B-tree]] and [[hash table]] indexes, and four index access methods: generalized search trees ([[GiST]]), generalized [[inverted index]]es (GIN), Space-Partitioned GiST (SP-GiST)<ref name="SP-GiST" /> and [[Block Range Index]]es (BRIN). In addition, user-defined index methods can be created, although this is quite an involved process. Indexes in PostgreSQL also support the following features:
*'''[[Expression index]]es''' can be created with an index of the result of an expression or function, instead of simply the value of a column.
*'''[[Partial index]]es''', which only index part of a table, can be created by adding a <code>WHERE</code> clause to the end of the <code>CREATE INDEX</code> statement. This allows a smaller index to be created.
*'''[[Bitmap index]] scans''' are supported as of version 8.1. This involves reading multiple indexes and generating a bitmap that expresses their [[intersection (set theory)|intersection]] with the [[tuple]]s that match the selection criteria. This provides a way of composing indexes together; on a table with 20 columns, there are, in principle, 20[[factorial|!]] indexes that could be defined — which is far too many to actually use. If one index is created on each column, bitmap scans can compose arbitrary combinations of those indexes at query time for each column that seems worth considering as a constraint.


* [[Expression index]]es can be created with an index of the result of an expression or function, instead of simply the value of a column.
===Triggers===
* [[Partial index]]es, which only index part of a table, can be created by adding a WHERE clause to the end of the CREATE INDEX statement. This allows a smaller index to be created.
Triggers are events triggered by the action of SQL query. For example, an INSERT query might activate a trigger that checked if the values of the query were valid. Most triggers are only activated by either INSERT or UPDATE queries.
* The planner is able to use multiple indexes together to satisfy complex queries, using temporary in-memory [[bitmap index]] operations (useful for [[data warehouse]] applications for joining a large [[fact table]] to smaller [[dimension table]]s such as those arranged in a [[star schema]]).
* [[k-nearest neighbors algorithm|''k''-nearest neighbors]] (''k''-NN) indexing (also referred to KNN-GiST<ref name="KNN-GiST" />) provides efficient searching of "closest values" to that specified, useful to finding similar words, or close objects or locations with [[Geographic data and information|geospatial]] data. This is achieved without exhaustive matching of values.
* Index-only scans often allow the system to fetch data from indexes without ever having to access the main table.
* [[Block Range Index]]es (BRIN).


=== Schemas ===
[[Database trigger|Triggers]] are fully supported and can be attached to tables but not to views. Views can have rules, though. Multiple triggers are fired in alphabetical order. In addition to calling functions written in the native PL/PgSQL, triggers can also invoke functions written in other languages like PL/Perl. <!-- and others... -->
PostgreSQL schemas are [[namespace]]s, allowing objects of the same kind and name to co-exist in a single database.
They are not to be confused with a
[[database schema]] -- the abstract, structural, organizational specification which defines how every table's data relates to data within other tables.
All PostgreSQL database objects, except for a few global objects such as [[#Security|roles]] and [[tablespace]]s, exist within a schema.
They cannot be nested, schemas cannot contain schemas.
The permission system controls access to schemas and their content.
By default, newly created databases have only a single schema called ''public'' but other schemas can be added and the public schema isn't mandatory.


A {{code|search_path}} setting determines the order in which PostgreSQL checks schemas for unqualified objects (those without a prefixed schema). By default, it is set to {{code|$user, public}} ({{code|$user}} refers to the currently connected database user). This default can be set on a database or role level, but as it is a session parameter, it can be freely changed (even multiple times) during a client session, affecting that session only.
===MVCC===
PostgreSQL manages [[concurrency control|concurrency]] through a system known as [[Multiversion concurrency control|Multi-Version Concurrency Control]] (MVCC), which gives each user a "snapshot" of the database, allowing changes to be made without being visible to other users until a transaction is committed. This largely eliminates the need for read locks, and ensures the database maintains the [[ACID]] principles in an efficient manner.


Non-existent schemas, or other schemas not accessible to the logged-in user, that are listed in search_path are silently skipped during object lookup.
===Rules===
Rules allow the "query tree" of an incoming query to be rewritten. One common usage is to implement updatable views.


New objects are created in whichever valid schema (one that can be accessed) appears first in the search_path.
===Data types===
A wide variety of native [[datatype|data types]] are supported, including:
*[[Arbitrary precision]] numerics
*Unlimited length text
*Geometric primitives
*[[IP addresses|IP]] and [[IPv6]] addresses
*[[Classless Inter-Domain Routing|CIDR]] blocks, and [[MAC address]] data types
*Arrays


=== Data types ===
In addition, users can create their own data types which can usually be made fully indexable via PostgreSQL's [[GiST]] infrastructure.
A wide variety of native [[data type]]s are supported, including:


* Boolean
Examples of these are the [[Geographic information system]] (GIS) data types from the [[PostGIS]] project for PostgreSQL.
* [[Arbitrary-precision arithmetic|Arbitrary-precision]] numerics
* Character (text, varchar, char)
* Binary
* Date/time (timestamp/time with/without time zone, date, interval)
* Money
* Enum
* Bit strings
* Text search type
* Composite
* HStore, an extension enabled key-value store within PostgreSQL<ref>{{Cite web |url=https://www.linuxjournal.com/content/postgresql-nosql-database |title=PostgreSQL, the NoSQL Database &#124; Linux Journal |website=www.linuxjournal.com}}</ref>
* Arrays ([[dynamic array|variable-length]] and can be of any data type, including text and composite types) up to 1&nbsp;GB in total storage size
* Geometric primitives
* [[IPv4]] and [[IPv6]] addresses
* [[Classless Inter-Domain Routing]] (CIDR) blocks and [[MAC address]]es
* [[XML]] supporting [[XPath]] queries
* [[Universally unique identifier]] (UUID)
* JavaScript Object Notation ([[JSON]]), and a faster [[binary code|binary]] JSONB (not the same as [[BSON]]<ref name="jsonb" />)


In addition, users can create their own data types which can usually be made fully indexable via PostgreSQL's indexing infrastructures{{snd}} GiST, GIN, SP-GiST. Examples of these include the [[geographic information system]] (GIS) data types from the [[PostGIS]] project for PostgreSQL.
===User-defined objects===

There is also a data type called a ''domain'', which is the same as any other data type but with optional constraints defined by the creator of that domain. This means any data entered into a column using the domain will have to conform to whichever constraints were defined as part of the domain.

A data type that represents a range of data can be used which are called range types. These can be discrete ranges (e.g. all integer values 1 to 10) or continuous ranges (e.g., any time between {{nowrap|10:00 am}} and {{nowrap|11:00 am}}). The built-in range types available include ranges of integers, big integers, decimal numbers, time stamps (with and without time zone) and dates.

Custom range types can be created to make new types of ranges available, such as IP address ranges using the inet type as a base, or float ranges using the float data type as a base. Range types support inclusive and exclusive range boundaries using the {{kbd|[]}} and {{kbd|()}} characters respectively. (e.g., {{code|[4,9)}} represents all integers starting from and including 4 up to but not including 9.) Range types are also compatible with existing operators used to check for overlap, containment, right of etc.

=== User-defined objects ===
New types of almost all objects inside the database can be created, including:
New types of almost all objects inside the database can be created, including:

* Indices
* Operators (existing ones can be [[operator overloading|overloaded]])
* [[Aggregate function]]s
* [[Data domain|Domains]]
* Casts
* Casts
* Conversions
* Conversions
* Data types
* [[Data domain]]s
* Functions, including aggregate functions and window functions
* Indexes including custom indexes for custom types
* Operators (existing ones can be [[Operator overloading|overloaded]])
* Procedural languages


===Inheritance===
=== Inheritance ===
Tables can be set to inherit their characteristics from a "parent" table. Data is shared between "parent" and "child(ren)" tables. Tuples inserted or deleted in the "child" table will respectively be inserted or deleted in the "parent" table. Also adding a column in the parent table will cause that column to appear in the child table as well. This feature is not fully supported yet—in particular, table constraints are not currently inheritable. This means that attempting to insert the id of a row from a child table into table that has a foreign key constraint referencing a parent table will fail because Postgres doesn't recognize that the id from the child table is also a valid id in the parent table.
Tables can be set to inherit their characteristics from a ''parent'' table. Data in child tables will appear to exist in the parent tables, unless data is selected from the parent table using the ONLY keyword, i.e. {{code|lang="sql" | SELECT * FROM ONLY parent_table;}}. Adding a column in the parent table will cause that column to appear in the child table.


Inheritance provides a way to map the features of generalization hierarchies depicted in Entity Relationship Diagrams (ERD) directly into the PostgreSQL database.
Inheritance can be used to implement table partitioning, using either triggers or rules to direct inserts to the parent table into the proper child tables.
<!-- Verify and add type inheritance sentences from above -->


This feature is not fully supported. In particular, table constraints are not currently inheritable. All check constraints and not-null constraints on a parent table are automatically inherited by its children. Other types of constraints (unique, primary key, and foreign key constraints) are not inherited.
===Other features===
*[[Referential integrity]] [[constraint]]s including [[foreign key]] constraints, column constraints, and row checks
*[[View (database)|View]]s While updateable views have not been implemented, the same functionality can be achieved using the rules system.
*Full, inner, and outer (left and right) [[join (SQL)|join]]s
*Sub-[[select (SQL)|select]]s
*[[database transaction|Transaction]]s
*Supports most of the major features of [[SQL:2003]] standard [http://developer.postgresql.org/pgdocs/postgres/features.html] [http://developer.postgresql.org/pgdocs/postgres/unsupported-features-sql-standard.html unsupported] [http://developer.postgresql.org/pgdocs/postgres/features-sql-standard.html supported] <-- lead to documentation for the ''next'' release of PostgreSQL, follow [http://www.postgresql.org/docs/manuals/ this link] to find manuals for ''already released'' versions of PostgreSQL
*Encrypted connections via [[Secure Sockets Layer|SSL]]
*Binary and textual large-object storage
*Online backup
*[[Data domain|Domains]]
*[[Tablespace]]s
*[[Savepoint]]s
*[[Point-in-time recovery]]
*[[Two-phase commit]]
*TOAST ('''T'''he '''O'''versized-'''A'''ttribute '''S'''torage '''T'''echnique) is used to transparently store large table attributes (such as big MIME attachments or XML messages) in a separate area, with automatic compression.
*[[Regular expression]]s [http://www.oreillynet.com/pub/a/databases/2006/02/02/postgresq_regexes.html]


Inheritance provides a way to map the features of generalization hierarchies depicted in [[entity–relationship model|entity relationship diagrams]] (ERDs) directly into the PostgreSQL database.
===Add-ons===
*Geographic objects via [[PostGIS]]. GPL.
*[[Full text search]] via [http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/ Tsearch2] and [[OpenFTS]]. GPL.
*Several asynchronous master/slave replication packages, including
**[http://www.slony.info Slony-I] (BSD license)
**[http://www.pgcluster.org/ pgcluster] (BSD license)
**[http://www.commandprompt.com/products/mammothreplicator Mammoth Replicator].
*XML/XSLT support via [http://www.throwingbeans.org/postgresql_and_xml.html XPath Extensions in the contrib section]. GPL.


=== Other storage features ===
==Benchmarks==
* [[Referential integrity]] constraints including [[foreign key]] constraints, column [[Constraint satisfaction|constraints]], and row checks
Many informal performance studies of PostgreSQL have been done<ref name=BERKUS>{{cite web |author=[[Josh Berkus]] |date=2007-07-06 |title=PostgreSQL publishes first real benchmark |url=http://blogs.ittoolbox.com/database/soup/archives/postgresql-publishes-first-real-benchmark-17470 |accessdate=2007-07-10 }}</ref> but the first industry-standard and peer-validated benchmark was completed in June 2007 using the Sun Java Systems Application Server 9.0 Platform Edition and Postgres 8.2<ref name=SPECJ>{{cite web |publisher=[[SPEC]] |date=2007-07-06 |title=SPECjAppServer®2004 Result |url=http://www.spec.org/jAppServer2004/results/res2007q3/jAppServer2004-20070606-00065.html |accessdate=2007-07-10 }}</ref>. This result of 778.14 SPECjAppServer2004 JOPS@Standard compares favourably with the 874 JOPS@Standard with Oracle 10 on an Itanium based HP-UX<ref name=BERKUS>{{cite web |author=[[Josh Berkus]] |date=2007-07-06 |title=PostgreSQL publishes first real benchmark |url=http://blogs.ittoolbox.com/database/soup/archives/postgresql-publishes-first-real-benchmark-17470 |accessdate=2007-07-10 }}</ref>
* Binary and textual large-object storage
* [[Tablespace]]s
* Per-column collation
* Online backup
* Point-in-time recovery, implemented using write-ahead logging
* In-place upgrades with pg_upgrade for less downtime<!-- (supports upgrades from 8.3.x<ref>{{Cite web|title=PostgreSQL: Documentation: 9.0: pg_upgrade|url=https://www.postgresql.org/docs/9.0/pgupgrade.html|access-date=2020-06-09|website=www.postgresql.org}}</ref> and later) -->


== Control and connectivity ==
==Prominent users==
<!-- http://www.postgresql.org/about/users -->
* [[.org]], [[.info]], [[.mobi]] and [[.aero]] domain registry via [[Afilias]] [http://www.computerworld.com.au/index.php?id=760310963]
* The [[American Chemical Society]]
* [[BASF]]
* Chicagocrime.org [http://www.holovaty.com/blog/archive/2006/04/07/0927]
* [[IMDB]]
* [[Skype]]
* [[TiVo]]
* [[Penny Arcade (webcomic)|Penny Arcade]]
* [[Sony Online]] [http://www.computerworld.com/databasetopics/data/software/story/0,10801,109722,00.html]
* [[U.S. Department of Labor]]
* [[USPS]]
* [[VeriSign]]
* [[Wisconsin Circuit Court Access]] with 6 * 180GB DBs replicated in real time
* [[OpenACS]] and [[.LRN]]
* [[Symantec]] (PostgreSQL is the data store for the Veritas NetBackup PureDisk [http://www.symantec.com/enterprise/products/overview.jsp?pcid=1018&pvid=1381_1] product)


=== Foreign data wrappers ===
==References==
PostgreSQL can link to other systems to retrieve data via foreign data wrappers (FDWs).<ref>{{cite book
* {{cite book|title=Beginning Databases with PostgreSQL|edition=Second Edition|first=Neil|last=Matthew|coauthors=Stones, Richard|id=ISBN 1-59059-478-9 }}
|last1=Obe
* {{cite book|title=Beginning PHP and PostgreSQL 8: From Novice to Professional|first=W. Jason|last=Gilmore|coauthors=Treat, Robert|id=ISBN 1-59059-547-5 }}
|first1=Regina
* {{cite book|title=Practical PostgreSQL|first=John C.|last=Worsley|coauthors=Drake, Joshua D.|id=ISBN 1-56592-846-6 |url=http://www.commandprompt.com/ppbook/}}
|last2=Hsu
* {{cite book|title=PostgreSQL|first=Korry|last=Douglas|id=ISBN 0-672-32756-2 }}
|first2=Leo S.
|chapter=10: Replication and External Data
|title=PostgreSQL: Up and Running
|url=https://books.google.com/books?id=Q8jkIZkMTPcC
|edition=1
|location=Sebastopol, CA
|publisher=[[O'Reilly Media|O'Reilly Media, Inc.]]
|date=2012
|page=129
|isbn=978-1-4493-2633-3
|access-date=October 17, 2016
|quote=Foreign Data Wrappers (FDW) [...] are mechanisms of querying external datasources. PostgreSQL 9.1 introduced this [[SQL/MED]] standards compliant feature.
}}</ref>
These can take the form of any data source, such as a file system, another [[relational database]] management system (RDBMS), or a web service. This means that regular database queries can use these data sources like regular tables, and even join multiple data-sources together.


=== Notes ===
=== Interfaces ===
PostgreSQL supports a binary [[communication protocol]] that allows applications to connect to the database server. The protocol is versioned (currently 3.0, as of PostgreSQL 7.4) and has a detailed specification.<ref>{{cite web
{{reflist}}
| url = https://www.postgresql.org/docs/current/protocol.html
| title = Frontend/Backend Protocol
| author = <!--Not stated-->
| website = postgresql.org
| date = November 9, 2023
| access-date = 2023-12-17
| quote = This document describes version 3.0 of the protocol, implemented in PostgreSQL 7.4 and later.
}}</ref>


The official client implementation of this communication protocol is a [[C (programming language)|C]] [[API]], libpq.<ref>{{cite web
==External links==
| url = https://www.postgresql.org/docs/16/libpq.html
{{ External links | January 2007 }}
| title = libpq
===About PostgreSQL===
| author = <!--Not stated-->
*[http://www.pervasivepostgres.com/postgresql/pgd/index.asp PostgreSQL Universe] Comprehensive (Link-)Directory
| website = postgresql.org
*{{dmoz|Computers/Software/Databases/PostgreSQL}}
| date = November 9, 2023
*[http://www.planetpostgresql.org Planet PostgreSQL], blog aggregator
| access-date = 2023-12-17
*[http://osdb.org/ Open Source Database Network]
}}</ref> In addition, the officially supported [[ECPG]] tool allows SQL commands to be embedded in C code.<ref>{{cite web
*[http://www.databasejournal.com/features/postgresql/ Database Journal articles on PostgreSQL]
| url = https://www.postgresql.org/docs/16/ecpg.html
*[http://www.troubleshooters.com/lpm/200301/200301.htm Linux Productivity Magazine: a complete issue on PostgreSQL]
| title = Embedded SQL in C
*[http://searchopensource.techtarget.com/originalContent/0,289142,sid39_gci1172668,00.html a rebuttal] to the FUD (fear, uncertainty, and doubt) surrounding much of the criticism against PostgreSQL.
| author = <!--Not stated-->
*[http://sql-info.de/postgresql/postgres-gotchas.html PostgreSQL gotchas], documented but counterintuitive behavior
| website = postgresql.org
*[http://www.kenjennings.cc/st/stprgux.html#test_pgc Test_PGC], Example embedded SQL/C program for PostgreSQL showing database operations and SQLSTATE testing.
| date = November 9, 2023
| access-date = 2023-12-17
}}</ref> Both are part of the standard PostgreSQL distribution.<ref>{{cite web
| url = https://www.postgresql.org/docs/16/client-interfaces.html
| title = Client Interfaces
| author = <!--Not stated-->
| website = postgresql.org
| date = November 9, 2023
| access-date = 2023-12-17
}}</ref>


Third-party libraries for connecting to PostgreSQL are available for many [[programming language]]s, including [[C++]],<ref>{{cite web|title=libpqxx|url=http://pqxx.org/development/libpqxx/|access-date=April 4, 2020}}</ref> [[Java (programming language)|Java]],<ref>{{cite web|title=PostgreSQL JDBC Driver|url=https://jdbc.postgresql.org/|access-date=April 4, 2020}}</ref> [[Julia (programming language)|Julia]],<ref>{{Cite web|date=2021-06-30|title=[ANN] PostgresORM.jl: Object Relational Mapping for PostgreSQL|url=https://discourse.julialang.org/t/ann-postgresorm-jl-object-relational-mapping-for-postgresql/63847|access-date=2021-08-26|website=JuliaLang|language=en}}</ref><ref>{{Cite web|title=GitHub - invenia/LibPQ.jl: A Julia wrapper for libpq|url=https://github.com/invenia/LibPQ.jl|access-date=2021-08-26|website=GitHub|language=en}}</ref><ref name="PL/Julia" /> [[Python (programming language)|Python]],<ref name="psycopg2" /> [[Node.js]],<ref>{{cite web|title=node-postgres|url=https://node-postgres.com/|access-date=April 4, 2020}}</ref> [[Go (programming language)|Go]],<ref>{{cite web |title=SQL database drivers |url=https://github.com/golang/go/wiki/SQLDrivers#drivers |website=Go wiki |publisher=golang.org |access-date=June 22, 2015}}</ref> and [[Rust (programming language)|Rust]].<ref>{{cite web|title=Rust-Postgres|url=https://crates.io/crates/postgres|access-date=April 4, 2020}}</ref>
=== External PostgreSQL-related projects ===


=== Procedural languages ===
The developers of PostgreSQL try to keep the system itself down to a set of "core" features, rather than encouraging extensions to be rolled into the main system. Here are places where "secondary" projects are managed:
Procedural languages allow developers to extend the database with custom [[subroutine]]s (functions), often called ''[[stored procedure]]s''. These functions can be used to build [[database trigger]]s (functions invoked on modification of certain data) and custom data types and [[aggregate function]]s.<ref>{{cite web|url=https://www.postgresql.org/docs/current/server-programming.html|title=Server Programming|access-date=19 May 2019|website=PostgreSQL documentation}}</ref> Procedural languages can also be invoked without defining a function, using a DO command at SQL level.<ref>{{cite web|url=https://www.postgresql.org/docs/current/sql-do.html|title=DO|access-date=19 May 2019|website=PostgreSQL documentation}}</ref>


Languages are divided into two groups: Procedures written in ''safe'' languages are [[Sandbox (computer security)|sandboxed]] and can be safely created and used by any user. Procedures written in ''unsafe'' languages can only be created by [[superuser]]s, because they allow bypassing a database's security restrictions, but can also access sources external to the database. Some languages like Perl provide both safe and unsafe versions.
*[http://www.pgfoundry.org/ PgFoundry PostgreSQL-related projects]
*[http://sourceforge.net/softwaremap/trove_list.php?form_cat=525 SourceForge PostgreSQL-related projects]


PostgreSQL has built-in support for three procedural languages:
=== PostgreSQL documentation ===
*[http://www.postgresql.org/docs/faqs.FAQ.html PostgreSQL FAQ] (Frequently Asked Questions)
*[http://www.postgresql.org/ PostgreSQL Website]
*[http://www.postgresql.org/docs/ PostgreSQL Documentation]


* Plain SQL (safe). Simpler SQL functions can get [[inline expansion|expanded inline]] into the calling (SQL) query, which saves function call overhead and allows the query optimizer to "see inside" the function.
* Procedural Language/PostgreSQL ([[PL/pgSQL]]) (safe), which resembles Oracle's Procedural Language for SQL ([[PL/SQL]]) procedural language and SQL/Persistent Stored Modules ([[SQL/PSM]]).
* [[C (programming language)|C]] (unsafe), which allows loading one or more custom [[shared library]] into the database. Functions written in C offer the best performance, but bugs in code can crash and potentially corrupt the database. Most built-in functions are written in C.

In addition, PostgreSQL allows procedural languages to be loaded into the database through extensions. Three language extensions are included with PostgreSQL to support [[Perl]], [[Tcl]], and [[Python (programming language)|Python]]. For Python, the current {{nowrap|Python 3}} is used, and the discontinued {{nowrap|Python 2}} is no longer supported as of PostgreSQL 15. Both were supported previously, defaulting to {{nowrap|Python 2}}, while old and new versions couldn't be used in the same session.<ref>{{cite web|url=https://www.postgresql.org/docs/current/plpython.html|title=PL/Python - Python Procedural Language|access-date=October 23, 2022|website=PostgreSQL documentation}}</ref> External projects provide support for many other languages,<ref>{{cite web |date=March 31, 2016 |title=Procedural Languages |publisher=postgresql.org |url=https://www.postgresql.org/docs/current/static/external-pl.html |access-date=April 7, 2016}}</ref> including PL/[[Java (programming language)|Java]], [[JavaScript]] (PL/V8), PL/[[Julia (programming language)|Julia]],<ref name="PL/Julia">{{Cite web|date=2020-03-08|title=PL/Julia extension ( minimal )|url=https://discourse.julialang.org/t/pl-julia-extension-minimal/34232/2|access-date=2021-08-26|website=JuliaLang|language=en}}</ref> PL/[[R (programming language)|R]],<ref>{{Cite web|url=https://github.com/postgres-plr/plr|title=postgres-plr/plr|date=June 17, 2021|via=GitHub}}</ref> PL/[[Ruby (programming language)|Ruby]], and others.

=== Triggers ===
Triggers are events triggered by the action of SQL [[data manipulation language]] (DML) statements. For example, an [[Insert (SQL)|INSERT]] statement might activate a trigger that checks if the values of the statement are valid. Most triggers are only activated by either INSERT or [[Update (SQL)|UPDATE]] statements.

Triggers are fully supported and can be attached to tables. Triggers can be per-column and conditional, in that UPDATE triggers can target specific columns of a table, and triggers can be told to execute under a set of conditions as specified in the trigger's WHERE clause. Triggers can be attached to [[View (SQL)|views]] by using the INSTEAD OF condition. Multiple triggers are fired in alphabetical order. In addition to calling functions written in the native PL/pgSQL, triggers can also invoke functions written in other languages like PL/Python or PL/Perl.

=== Asynchronous notifications ===
PostgreSQL provides an asynchronous messaging system that is accessed through the NOTIFY, LISTEN and UNLISTEN commands. A session can issue a NOTIFY command, along with the user-specified channel and an optional payload, to mark a particular event occurring. Other sessions are able to detect these events by issuing a LISTEN command, which can listen to a particular channel. This functionality can be used for a wide variety of purposes, such as letting other sessions know when a table has updated or for separate applications to detect when a particular action has been performed. Such a system prevents the need for continuous [[polling (computer science)|polling]] by applications to see if anything has yet changed, and reducing unnecessary overhead. Notifications are fully transactional, in that messages are not sent until the transaction they were sent from is committed. This eliminates the problem of messages being sent for an action being performed which is then rolled back.

Many connectors for PostgreSQL provide support for this notification system (including libpq, JDBC, Npgsql, psycopg and node.js) so it can be used by external applications.

PostgreSQL can act as an effective, persistent [[publish–subscribe pattern|"pub/sub" server]] or job server by combining LISTEN with FOR UPDATE SKIP LOCKED.<ref name="postgres-jobserver">{{cite web |last1=Chartier |first1=Colin |title=System design hack: Postgres is a great pub/sub & job server |url=https://layerci.com/blog/postgres-is-the-answer/ |website=LayerCI blog |date=November 8, 2019 |access-date=November 24, 2019}}</ref><ref name="release-9.5">{{cite web |title=Release 9.5 |url=https://www.postgresql.org/docs/9.5/release-9-5.html |website=postgresql.org|date=February 11, 2021 }}</ref><ref name="ringer-skip-locked">{{cite web |last1=Ringer |first1=Craig |title=What is SKIP LOCKED for in PostgreSQL 9.5? |url=https://www.2ndquadrant.com/en/blog/what-is-select-skip-locked-for-in-postgresql-9-5/ |website=2nd Quadrant |date=April 13, 2016 |access-date=November 24, 2019}}</ref>

=== Rules ===
Rules allow the "query tree" of an incoming query to be rewritten; they are an, automatically invoked, [[Macro (computer science)|macro language]] for SQL. "Query Re-Write Rules" are attached to a table/class and "Re-Write" the incoming DML (select, insert, update, and/or delete) into one or more queries that either replace the original DML statement or execute in addition to it. Query Re-Write occurs after DML statement parsing and before query planning.

The functionality rules provide was, in almost every way, later duplicated with the introduction of newer types of triggers.
The use of triggers is usually preferred over rules as it is easier to reason about trigger behavior and interactions than when equivalent rules are used.

=== Other querying features ===
* [[Database transaction|Transactions]]
* [[Full-text search]]
* Views
** Materialized views<ref name="materialized_views" />
** Updateable views<ref name="updatable_views" />
** Recursive views<ref name="recursive_views" />
* Inner, outer (full, left, and right), and cross [[Join (SQL)|joins]]
* Sub-[[Select (SQL)|selects]]
** Correlated sub-queries<ref name="Introduction and Concepts" />
* [[Regular expression]]s<ref name="Bernier" />
* [[Hierarchical and recursive queries in SQL#Common table expression|Common table expressions]] and writable common table expressions
* Encrypted connections via [[Transport Layer Security]] (TLS); current versions do not use vulnerable SSL, even with that configuration option<ref name="POODLE" />
* Domains
* [[Savepoint]]s
* [[Two-phase commit protocol|Two-phase commit]]
* The Oversized-Attribute Storage Technique (TOAST) is used to transparently store large table attributes (such as big MIME attachments or XML messages) in a separate area, with automatic compression.
* [[Embedded SQL]] is implemented using preprocessor. SQL code is first written embedded into C code. Then code is run through ECPG preprocessor, which replaces SQL with calls to code library. Then code can be compiled using a C compiler. Embedding works also with [[C++]] but it does not recognize all C++ constructs.

=== Concurrency model ===
PostgreSQL server is [[process (computing)|process]]-based (not threaded), and uses one operating system process per database session. Multiple sessions are automatically spread across all available CPUs by the operating system. Many types of queries can also be parallelized across multiple background worker processes, taking advantage of multiple CPUs or cores.<ref>{{Cite web |url=https://lwn.net/Articles/689387/ |title=PostgreSQL 9.6 Beta and PGCon 2016 |last=Berkus |first=Josh |date=June 2, 2016 |website=LWN.net}}</ref> Client applications can use threads and create multiple database connections from each thread.<ref>{{Cite web |url=https://wiki.postgresql.org/wiki/FAQ#How_does_PostgreSQL_use_CPU_resources.3F |title=FAQ – PostgreSQL wiki |website=wiki.postgresql.org |language=en |access-date=April 13, 2017}}</ref>

== Security ==
PostgreSQL manages its internal security on a per-[[Role-oriented programming|role]] basis. A role is generally regarded to be a user (a role that can log in), or a group (a role of which other roles are members). Permissions can be granted or revoked on any object down to the column level, and can allow or prevent the visibility/creation/alteration/deletion of objects at the database, [[#Schemas|schema]], table, and row levels.

PostgreSQL's SECURITY LABEL feature (extension to SQL standards), allows for additional security; with a bundled loadable module that supports label-based [[mandatory access control]] (MAC) based on [[Security-Enhanced Linux]] (SELinux) security policy.<ref>{{Cite web |url=https://wiki.postgresql.org/wiki/SEPostgreSQL_Documentation |title=SEPostgreSQL Documentation – PostgreSQL wiki |website=wiki.postgresql.org}}</ref><ref>{{Cite web |url=https://selinuxproject.org/page/NB_SQL_9.3 |title=NB SQL 9.3 - SELinux Wiki |website=selinuxproject.org}}</ref><!--through the use of "sepgsql extension"; provided in all supported versions; in "contrib"<ref>https://www.postgresql.org/docs/current/static/sepgsql.html {{Bare URL inline|date=March 2022}}</ref>).-->

PostgreSQL natively supports a broad number of external authentication mechanisms, including:

* Password: either [[Salted Challenge Response Authentication Mechanism|SCRAM-SHA-256]],<ref>{{cite web |title = PostgreSQL 10 Documentation: Appendix E. Release Notes |date=August 12, 2021|url=https://www.postgresql.org/docs/10/release-10.html#id-1.11.6.16.3}}</ref> [[MD5]] or plain-text
* [[Generic Security Services Application Program Interface]] (GSSAPI)
* [[Security Support Provider Interface]] (SSPI)
* [[Kerberos (protocol)|Kerberos]]
* [[Ident protocol|ident]] (maps O/S user-name as provided by an ident server to database user-name)
* Peer (maps local user name to database user name)
* [[Lightweight Directory Access Protocol]] (LDAP)
** [[Active Directory]] (AD)
* [[RADIUS]]
* Certificate
* [[Pluggable authentication module]] (PAM)

The GSSAPI, SSPI, Kerberos, peer, ident and certificate methods can also use a specified "map" file that lists which users matched by that authentication system are allowed to connect as a specific database user.

These methods are specified in the cluster's host-based authentication configuration file (<kbd>pg_hba.conf</kbd>), which determines what connections are allowed. This allows control over which user can connect to which database, where they can connect from (IP address, IP address range, domain socket), which authentication system will be enforced, and whether the connection must use [[Transport Layer Security]] (TLS).

== Standards compliance ==
PostgreSQL claims high, but not complete, conformance with the latest [[SQL|SQL standard]] ("as of the version 15 release in October 2022, PostgreSQL conforms to at least 170 of the 179 mandatory features for [[SQL:2016]] Core conformance", and no other databases fully conformed to it<ref>{{Cite web|title=PostgreSQL: About|url=https://www.postgresql.org/about/|access-date=2021-08-26|website=www.postgresql.org}}</ref>). One exception is the handling of unquoted identifiers like table or column names. In PostgreSQL they are folded, internally, to lower case characters<ref name="identifiers"/> whereas the standard says that unquoted identifiers should be folded to upper case. Thus, {{code|Foo}} should be equivalent to {{code|FOO}} not {{code|foo}} according to the standard. Other shortcomings concern the absence of temporal tables allowing automatic logging of row versions during transactions with the possibility of browsing in time (FOR SYSTEM TIME predicate),{{citation needed |date=February 2022}} although relatively SQL compliant third-party extensions are available.<ref name="temporal-extensions" />

== Benchmarks and performance ==
{{Update|date=April 2024|reason=Performance information based on soft- and hardware of 9 years ago is basically useless|part=section|updated=2015-06-01}}
Many informal performance studies of PostgreSQL have been done.<ref name="Berkus" /> Performance improvements aimed at improving scalability began heavily with version 8.1. Simple benchmarks between version 8.0 and version 8.4 showed that the latter was more than ten times faster on read-only workloads and at least 7.5 times faster on both read and write workloads.<ref name="Vilmos" />

The first industry-standard and peer-validated benchmark was completed in June 2007, using the Sun Java System Application Server (proprietary version of [[GlassFish]]) 9.0 Platform Edition, [[UltraSPARC T1]]-based [[Sun Fire]] server and PostgreSQL 8.2.<ref name="SPECJ" /> This result of 778.14 SPECjAppServer2004 JOPS@Standard compares favourably with the 874 JOPS@Standard with Oracle 10 on an [[Itanium]]-based [[HP-UX]] system.<ref name="Berkus" />

In August 2007, Sun submitted an improved benchmark score of 813.73 SPECjAppServer2004 JOPS@Standard. With the [[system under test]] at a reduced price, the price/performance improved from $84.98/JOPS to $70.57/JOPS.<ref name="SPECjAppServer2004" />

The default configuration of PostgreSQL uses only a small amount of dedicated memory for performance-critical purposes such as caching database blocks and sorting. This limitation is primarily because older operating systems required kernel changes to allow allocating large blocks of [[shared memory]].<ref name="Kernel Resources" /> PostgreSQL.org provides advice on basic recommended performance practice in a [[wiki]].<ref name="pg9hiperf" />

In April 2012, Robert Haas of EnterpriseDB demonstrated PostgreSQL 9.2's linear CPU scalability using a server with 64 cores.<ref name="Haas" />

Matloob Khushi performed benchmarking between PostgreSQL 9.0 and MySQL 5.6.15 for their ability to process genomic data. In his performance analysis he found that PostgreSQL extracts overlapping genomic regions eight times faster than MySQL using two datasets of 80,000 each forming random human DNA regions. Insertion and data uploads in PostgreSQL were also better, although general searching ability of both databases was almost equivalent.<ref>{{cite journal |first=Matloob |last=Khushi |pmid=25560631 |title=Benchmarking database performance for genomic data |journal=J Cell Biochem |date=June 2015 |volume=116 |issue=6 |doi=10.1002/jcb.25049 |pages=877–83|arxiv=2008.06835 |s2cid=27458866 }}</ref>

== Platforms ==
PostgreSQL is available for the following operating systems: [[Linux]] (all recent distributions), [[64-bit computing|64-bit]] [[AArch64|ARM]] and [[x86-64]] installers available and tested for [[macOS]] (OS X)<ref name="OS X" /> version 10.12 and newer, [[Microsoft Windows|Windows]] (with installers available and tested for 64-bit [[Windows Server 2019]] and 2016; some older PostgreSQL versions were tested back to [[Windows Server 2012 R2|Windows 2012 R2]]<ref>{{Cite web|url=https://www.postgresql.org/download/windows/|title=PostgreSQL: Windows installers|website=www.postgresql.org|access-date=2021-08-26}}</ref>), <!-- too much detail? And maybe outdated: compilable by e.g. [[Microsoft Visual Studio|Visual Studio]], version 2013 up to the most recent 2019 version)--> [[FreeBSD]], [[OpenBSD]],<ref name=openbsd>{{cite web |url=http://ports.su/databases/postgresql,-main |title=postgresql-client-10.5p1 – PostgreSQL RDBMS (client) |work=[[OpenBSD ports]] |date=October 4, 2018 |access-date=October 10, 2018}}</ref> [[NetBSD]], and these without official (though unofficial likely available) binary executables, [[Solaris (operating system)|Solaris]],<!-- [[OpenIndiana]],<ref name="OpenIndiana" /> --><ref>{{Cite web |title=Installing and Configuring PostgreSQL - Oracle Solaris Cluster Data Service for PostgreSQL Guide |url=https://docs.oracle.com/cd/E19680-01/html/821-1534/ciajejfa.html |access-date=2023-02-04 |website=docs.oracle.com}}</ref> [[IBM AIX|AIX]], and [[HP-UX]].<ref>{{Cite web |title=HP-UX Porting and Archive Centre {{!}} postgresql-12.4 |url=http://hpux.connect.org.uk/hppd/hpux/Users/postgresql-12.4/ |access-date=2023-02-04 |website=hpux.connect.org.uk}}</ref> Most other (modern) Unix-like systems do also work.

PostgreSQL can be expected to work on any of the following [[instruction set architecture]]s (and operating systems): 64-bit [[x86-64]] and [[32-bit computing|32-bit]] [[x86]] on [[Windows XP]] (or later) and other operating systems; these are supported on other than Windows: 64-bit [[AArch64|ARM]]<ref name="AArch64" /> and the older 32-bit [[ARM architecture family|ARM]], including older such as [[ARMv6]] in [[Raspberry Pi]]<ref name=raspi />), [[z/Architecture]]<!-- aka S/390x in docs -->, [[IBM System/390|S/390]], [[PowerPC]] (incl. 64-bit [[Power ISA]]<!-- aka PowerPC 64-->), [[SPARC]] (also 64-bit), IA-64 [[Itanium]] ([[HP-UX]]), [[MIPS architecture|MIPS]] and [[PA-RISC]]. It was also known to work on some other platforms (while not been tested on for years, i.e. for latest versions).<ref name="SupportedPlatforms" />

== Database administration ==
{{See also|Comparison of database administration tools}}

Open source front-ends and tools for administering PostgreSQL include:

; {{anchor|psql}}psql: The primary [[Front and back ends|front-end]] for PostgreSQL is the {{code|psql}} [[command-line program]], which can be used to enter SQL queries directly, or execute them from a file. In addition, psql provides a number of meta-commands and various shell-like features to facilitate writing scripts and automating a wide variety of tasks; for example tab completion of object names and SQL syntax.
; {{anchor|pgAdmin}}pgAdmin: The pgAdmin package is a free and open-source [[graphical user interface]] (GUI) administration tool for PostgreSQL, which is supported on many computer platforms.<ref name="pgAdmin" /> The program is available in more than a dozen languages. The first prototype, named pgManager, was written for PostgreSQL 6.3.2 from 1998, and rewritten and released as pgAdmin under the GNU General Public License (GPL) in later months. The second incarnation (named pgAdmin II) was a complete rewrite, first released on January 16, 2002. The third version, pgAdmin III, was originally released under the [[Artistic License]] and then released under the same license as PostgreSQL. Unlike prior versions that were written in [[Visual Basic]], pgAdmin III is written in C++, using the [[wxWidgets]]<ref>{{cite web | url=https://packages.debian.org/jessie/pgadmin3 | title=Debian -- Details of package pgadmin3 in jessie | access-date=March 10, 2017}}</ref> framework allowing it to run on most common operating systems. The query tool includes a scripting language called pgScript for supporting admin and development tasks. In December 2014, Dave Page, the pgAdmin project founder and primary developer,<ref>{{cite web |title=pgAdmin Development Team |url=http://www.pgadmin.org/development/team.php |website=pgadmin.org |access-date=June 22, 2015}}</ref> announced that with the shift towards web-based models, work has begun on pgAdmin 4 with the aim to facilitate cloud deployments.<ref>{{cite web |last1=Dave |first1=Page |title=The story of pgAdmin |url=http://pgsnake.blogspot.co.uk/2014/12/the-story-of-pgadmin.html |website=Dave's Postgres Blog |publisher=pgsnake.blogspot.co.uk |access-date=December 7, 2014|date=December 7, 2014 }}</ref> In 2016, pgAdmin 4 was released. The pgAdmin 4 backend was written in [[Python (programming language)|Python]], using Flask and the [[Qt (software)|Qt framework]].<ref>{{cite web |title=pgAdmin 4 README |website=[[GitHub]] |url=https://github.com/postgres/pgadmin4/blob/master/README |access-date=August 15, 2018}}</ref>
; phpPgAdmin: phpPgAdmin is a web-based administration tool for PostgreSQL written in PHP and based on the popular [[phpMyAdmin]] interface originally written for [[MySQL]] administration.<ref name="PHPADMIN" />
; PostgreSQL Studio: PostgreSQL Studio allows users to perform essential PostgreSQL database development tasks from a web-based console. PostgreSQL Studio allows users to work with cloud databases without the need to open firewalls.<ref name="POSTGRESQLSTUDIO" />
; TeamPostgreSQL: AJAX/JavaScript-driven web interface for PostgreSQL. Allows browsing, maintaining and creating data and database objects via a web browser. The interface offers tabbed SQL editor with autocompletion, row editing widgets, click-through foreign key navigation between rows and tables, ''favorites'' management for commonly used scripts, among other features. Supports SSH for both the web interface and the [[database connection]]s. Installers are available for Windows, Macintosh, and Linux, and a simple cross-platform archive that runs from a script.<ref name="TEAMPOSTGRESQL" />
; LibreOffice, OpenOffice.org: [[LibreOffice]] and [[OpenOffice.org]] Base can be used as a front-end for PostgreSQL.<ref name="ooAsFrntEnd" /><ref name="loAsFrntEnd" />
; pgBadger: The pgBadger PostgreSQL log analyzer generates detailed reports from a PostgreSQL log file.<ref name="tuningPGinstance" />
; pgDevOps: pgDevOps is a suite of web tools to install & manage multiple PostgreSQL versions, extensions, and community components, develop SQL queries, monitor running databases and find performance problems.<ref>{{cite web |title=pgDevOps |url=https://www.bigsql.org/pgdevops/ |website=BigSQL.org |access-date=May 4, 2017 |archive-url=https://web.archive.org/web/20170401220832/http://www1.bigsql.org/pgdevops/ |archive-date=April 1, 2017 |url-status=dead}}</ref>
; Adminer: [[Adminer]] is a simple web-based administration tool for PostgreSQL and others, written in PHP.
; pgBackRest: pgBackRest is a backup and restore tool for PostgreSQL that provides support for full, differential, and incremental backups.<ref>{{Cite web|url=https://github.com/pgbackrest/pgbackrest|title=pgbackrest/pgbackrest|website=GitHub|date=November 21, 2021}}</ref>
; pgaudit: pgaudit is a PostgreSQL extension that provides detailed session and/or object audit logging via the standard logging facility provided by PostgreSQL.<ref>{{Cite web|url=https://github.com/pgaudit/pgaudit|title=pgaudit/pgaudit|website=GitHub|date=November 21, 2021}}</ref>
; WAL-E: WAL-E is a backup and restore tool for PostgreSQL that provides support for physical (WAL-based) backups, written in Python.<ref>{{Cite web|url=https://github.com/wal-e/wal-e|title=wal-e/wal-e|date=June 24, 2021|via=GitHub}}</ref>

A number of companies offer proprietary tools for PostgreSQL. They often consist of a universal core that is adapted for various specific database products. These tools mostly share the administration features with the open source tools but offer improvements in [[data modeling]], importing, exporting or reporting.

== Notable users ==
<!-- https://www.postgresql.org/about/users
Only add widely recognized organizations and products that use PostgreSQL as their *primary* database, and state specifically what they are using it for. Do *not* add new entries without providing comprehensive reliable sources; see [[Wikipedia:Reliable sources]] -->

Notable organizations and products that use PostgreSQL as the primary database include:

* [[Microsoft]], used for a petabyte-scale “Release Quality View” (RQV) analytics dashboard, which tracks quality of Windows updates analyzing 20K types of metrics from over 800M Windows devices.<ref name="Microsoft" />
* In 2009, the social-networking website [[Myspace]] used [[Aster Data Systems]]'s nCluster database for data warehousing, which was built on unmodified PostgreSQL.<ref name="Cecchet" /><ref name="Aster Data" />
* [[Geni.com]] uses PostgreSQL for their main genealogy database.<ref name="Geni" />
* [[OpenStreetMap]], a collaborative project to create a free editable map of the world.<ref name="OpenStreetMap" />
* [[Afilias]], domain registries for [[.org]], [[.info]] and others.<ref name="Afilias" /><ref name="begPHPpg-book"/>
* [[Sony Online]] multiplayer online games.<ref name="Sony Online" />
* [[BASF]], shopping platform for their agribusiness portal.<ref name="BASF" />
* [[Reddit]] social news website.<ref name="Reddit" />
* [[Skype]] VoIP application, central [[business]] databases.<ref>{{Cite web |url=https://wiki.postgresql.org/images/a/a9/Postgresql-at-skype.pdf |title=PostgreSQL @Skype |last=Pihlak |first=Martin |website=wiki.postgresql.org |access-date=January 16, 2019}}</ref>
* [[Sun xVM]], Sun's virtualization and datacenter automation suite.<ref name="xVM" />
* [[MusicBrainz]], open online music encyclopedia.<ref name="MusicBrainz" />
* The [[International Space Station]] – to collect telemetry data in orbit and replicate it to the ground.<ref name="ISS" />
* [[MyYearbook]] social-networking site.<ref name="MyYearbook" />
* [[Instagram]], a mobile photo-sharing service.<ref name="Instagram" />
* [[Disqus]], an online discussion and commenting service.<ref name="Disqus" />
* [[TripAdvisor]], travel-information website of mostly user-generated content.<ref name="TripAdvisor" />
* [[Yandex]], a Russian internet company switched its Yandex.Mail service from Oracle to Postgres.<ref>{{Cite web |url=https://news.ycombinator.com/item?id=12489055 |title=Yandex.Mail's successful migration from Oracle to Postgres [pdf] |website=Hacker News: news.ycombinator.com |access-date=September 28, 2016}}</ref>
* [[Amazon Redshift]], part of AWS, a columnar [[online analytical processing]] (OLAP) system based on [[ParAccel]]'s Postgres modifications.
* [[National Oceanic and Atmospheric Administration]]'s (NOAA) [[National Weather Service]] (NWS), Interactive Forecast Preparation System (IFPS), a system that integrates data from the [[NEXRAD]] [[weather radar]]s, surface, and [[hydrology]] systems to build detailed localized forecast models.<ref name="begPHPpg-book">{{cite book |author=W. Jason Gilmore |author2=R.H. Treat |title=Beginning PHP and PostgreSQL 8: From Novice to Professional |url=https://books.google.com/books?id=BiRC4JtQzFIC&pg=PA577 |access-date=August 30, 2017 |year=2006 |publisher=Apress |isbn=978-1-43020-136-6}}</ref><ref name="pg9AdminCookEdt2-book">{{cite book |author=S. Riggs |author2=G. Ciolli |author3=H. Krosing |author4=G. Bartolini |title=PostgreSQL 9 Administration Cookbook - Second Edition |url=https://books.google.com/books?id=rYrwCAAAQBAJ&pg=PA3 |access-date=September 5, 2017 |year=2015 |publisher=Packt |isbn=978-1-84951-906-9}}</ref>
* [[United Kingdom]]'s national weather service, [[Met Office]], has begun swapping Oracle for PostgreSQL in a strategy to deploy more open source technology.<ref name="pg9AdminCookEdt2-book"/><ref>{{Cite news |url=https://www.computerweekly.com/ezine/Computer-Weekly/The-Met-Office-turns-to-open-source/Met-Office-swaps-Oracle-for-PostgreSQL |title=Met Office swaps Oracle for PostgreSQL |website=computerweekly.com |date=June 17, 2014|access-date=September 5, 2017}}</ref>
* [[WhitePages.com]] had been using Oracle and [[MySQL]], but when it came to moving its core directories in-house, it turned to PostgreSQL. Because WhitePages.com needs to combine large sets of data from multiple sources, PostgreSQL's ability to load and index data at high rates was a key to its decision to use PostgreSQL.<ref name="begPHPpg-book"/>
* [[FlightAware]], a flight tracking website.<ref>{{cite web |title=Open Source Software |url=https://flightaware.com/about/code/ |website=FlightAware |access-date=November 22, 2017}}</ref>
* [[Grofers]], an online grocery delivery service.<ref>{{Cite news |url=https://lambda.grofers.com/ansible-at-grofers-part-2-managing-postgresql-c4069ce5855b |title=Ansible at Grofers (Part 2) — Managing PostgreSQL |date=February 28, 2017 |work=Lambda - The Grofers Engineering Blog |access-date=September 5, 2018}}</ref>
* ''[[The Guardian]]'' migrated from [[MongoDB]] to PostgreSQL in 2018.<ref>{{Cite news |last1=McMahon |first1=Philip |last2=Chiorean |first2=Maria-Livia |last3=Coleman |first3=Susie |last4=Askoolum |first4=Akash |url=https://www.theguardian.com/info/2018/nov/30/bye-bye-mongo-hello-postgres |title=Digital Blog: Bye bye Mongo, Hello Postgres |date=November 30, 2018 |work=[[The Guardian]] |language=en-GB |issn=0261-3077}}</ref>
* [[YugabyteDB]] implements the PostgreSQL query layer as its default SQL mode
* [[OpenAI]] uses PostgreSQL as part of its primary API service.<ref>{{Cite web |title=Elevated Errors on API and ChatGPT |url=https://status.openai.com/incidents/n254wyd7nml7 |access-date=December 2, 2023}}</ref>

== Service implementations ==
Some notable vendors offer PostgreSQL as [[software as a service]]:

* [[Heroku]], a [[platform as a service]] provider, has supported PostgreSQL since the start in 2007.<ref name="Heroku" /> They offer value-add features like full database ''roll-back'' (ability to restore a database from any specified time),<ref name="Darrow" /> which is based on WAL-E, open-source software developed by Heroku.<ref name="Kerstiens" />
* In January 2012, [[EnterpriseDB]] released a cloud version of both PostgreSQL and their own proprietary Postgres Plus Advanced Server with automated provisioning for failover, replication, load-balancing, and scaling. It runs on [[Amazon Web Services]].<ref name="Techweekeurope" /> Since 2015, Postgres Advanced Server has been offered as ApsaraDB for PPAS, a relational database as a service on Alibaba Cloud.<ref>{{Cite web|date=2018-09-26|title=Alibaba Cloud Expands Technical Partnership with EnterpriseDB|url=https://www.milestonepartners.com/alibaba-cloud-expands-technical-partnership-with-enterprisedb/|access-date=2020-06-09|website=Milestone Partners|language=en-US}}</ref>
* [[VMware]] has offered vFabric Postgres (also termed vPostgres<ref>{{cite book
|last1=O'Doherty
|first1=Paul
|last2=Asselin
|first2=Stephane
|chapter=3: VMware Workspace Architecture
|title=VMware Horizon Suite: Building End-User Services
|url=https://books.google.com/books?id=1mTYAwAAQBAJ
|series=VMware Press Technology
|location=Upper Saddle River, NJ
|publisher=VMware Press
|date=2014
|page=65
|isbn=978-0-13-347910-2
|access-date=September 19, 2016
|quote=In addition to the open source version of PostgreSQL, VMware offers vFabric Postgres, or vPostgres. vPostgres is a PostgreSQL virtual appliance that has been tuned for virtual environments.}}</ref>) for private clouds on [[VMware vSphere]] since May 2012.<ref name="Sargent" /> The company announced End of Availability (EOA) of the product in 2014.<ref>{{Cite web |date=1 September 2014 |title=VMware vFabric Suite EOA |url=https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/products/VMware-vFabric-Suite-EOA-FAQ.pdf |access-date=17 December 2023 }}</ref>
* In November 2013, [[Amazon Web Services]] announced the addition of PostgreSQL to their [[Amazon Relational Database Service|Relational Database Service]] offering.<ref name="aws.typepad.com" /><ref name="Williams" />
* In November 2016, [[Amazon Web Services]] announced the addition of PostgreSQL compatibility to their cloud-native [[Amazon Aurora]] managed database offering.<ref>{{Cite web |url=https://aws.amazon.com/blogs/aws/amazon-aurora-update-postgresql-compatibility/ |title=Amazon Aurora Update – PostgreSQL Compatibility |website=AWS Blog |access-date=December 1, 2016|date=November 30, 2016 }}</ref>
* In May 2017, [[Microsoft Azure]] announced Azure Databases for PostgreSQL.<ref>{{Cite web |url=https://azure.microsoft.com/en-us/blog/azure-database-for-mysql-public-preview/|title=Announcing Azure Database for PostgreSQL| website=Azure Blog|date=May 10, 2017 |access-date=June 19, 2019}}</ref>
* In May 2019, [[Alibaba Cloud]] announced PolarDB for PostgreSQL.<ref>{{Cite web|url=https://developpaper.com/aliyun-polardb-released-major-updates-to-support-one-click-migration-of-databases-such-as-oracle-to-the-cloud/|title=Aliyun PolarDB released major updates to support one-click migration of databases such as Oracle to the cloud|date=July 6, 2019|website=Develop Paper}}</ref>
* [[Jelastic]] [[Multicloud]] [[Platform as a Service]] has provided container-based PostgreSQL support since 2011. It also offers automated asynchronous master-slave replication of PostgreSQL.<ref name="Auto-Replication" />
* In June 2019, [[IBM Cloud]] announced IBM Cloud Hyper Protect DBaaS for PostgreSQL.<ref>{{Cite web|title=IBM Cloud Hyper Protect DBaaS for PostgreSQL documentation|url=https://cloud.ibm.com/docs/hyper-protect-dbaas-for-postgresql?topic=hyper-protect-dbaas-for-postgresql-gettingstarted|access-date=2020-06-24|website=cloud.ibm.com|language=en-us}}</ref>
* In September 2020, Crunchy Data announced Crunchy Bridge.<ref>{{Cite web|title=Crunchy Data Continues PostgreSQL Support with the Release of Crunchy Bridge|url=https://www.dbta.com/Editorial/News-Flashes/Crunchy-Data-Continues-PostgreSQL-Support-with-the-Release-of-Crunchy-Bridge-142951|date=September 18, 2020}}</ref>
* In June 2022, Neon.tech announced Neon Serverless Postgres.<ref>{{Cite web|title=SELECT 'Hello, World' Serverless Postgres built for the cloud|url=https://neon.tech/blog/hello-world|date=June 15, 2022}}</ref>

== Release history ==
{| class="wikitable"
|-
|+ Release history
|-
! scope="col" | Release
! scope="col" | First release
! scope="col" | Latest minor version
! scope="col" | Latest release
! scope="col" | End of<br />life<ref>{{cite web |title=Versioning policy |publisher=PostgreSQL Global Development Group |url=https://www.postgresql.org/support/versioning/ |access-date=October 4, 2018}}</ref>
! scope="col" | Milestones
|-
! scope="row" | 6.0
| style=white-space:nowrap | 1997-01-29
| {{NA}}
| {{NA}}
| {{NA}}
| First formal release of PostgreSQL, unique indexes, pg_dumpall utility, ident authentication
|-
! scope="row" | 6.1
| style=white-space:nowrap | 1997-06-08
| {{Version |o |6.1.1 |style=text-align:center; white-space:nowrap}}
| 1997-07-22
| {{NA}}
| Multicolumn indexes, sequences, money data type, GEQO (GEnetic Query Optimizer)
|-
! scope="row" | 6.2
| 1997-10-02
| {{Version |o |6.2.1 |style=text-align:center}}
| 1997-10-17
| {{NA}}
| JDBC interface, triggers, server programming interface, constraints
|-
! scope="row" | 6.3
| 1998-03-01
| {{Version |o |6.3.2 |style=text-align:center}}
| 1998-04-07
| 2003-03-01
| SQL-92 subselect ability, PL/pgTCL
|-
! scope="row" | 6.4
| 1998-10-30
| {{Version |o |6.4.2 |style=text-align:center}}
| 1998-12-20
| 2003-10-30
| VIEWs (then only read-only) and RULEs, [[PL/pgSQL]]
|-
! scope="row" | 6.5
| 1999-06-09
| {{Version |o |6.5.3 |style=text-align:center}}
| style=white-space:nowrap | 1999-10-13
| style=white-space:nowrap | 2004-06-09
| [[Multiversion concurrency control|MVCC]], temporary tables, more SQL statement support (CASE, INTERSECT, and EXCEPT)
|-
! scope="row" | 7.0
| 2000-05-08
| {{Version |o |7.0.3 |style=text-align:center}}
| 2000-11-11
| 2004-05-08
| Foreign keys, SQL-92 syntax for joins
|-
! scope="row" | 7.1
| 2001-04-13
| {{Version |o |7.1.3 |style=text-align:center}}
| 2001-08-15
| 2006-04-13
| Write-ahead log, outer joins
|-
! scope="row" | 7.2
| 2002-02-04
| {{Version |o |7.2.8 |style=text-align:center}}
| 2005-05-09
| 2007-02-04
| PL/Python, [[Object identifier|OIDs]] no longer required, [[Internationalization and localization|internationalization]] of messages
|-
! scope="row" | 7.3
| 2002-11-27
| {{Version |o |7.3.21 |style=text-align:center}}
| 2008-01-07
| 2007-11-27
| Schema, table function, [[prepared query]]<ref>{{cite magazine |first=Lisa |last=Vaas |date=December 2, 2002 |title=Databases Target Enterprises |url=https://www.eweek.com/c/a/Database/Databases-Target-Enterprises |magazine=[[eWeek]] |access-date=October 29, 2016}}</ref>
|-
! scope="row" | 7.4
| 2003-11-17
| {{Version |o |7.4.30 |style=text-align:center}}
| 2010-10-04
| 2010-10-01
| Optimization on JOINs and [[data warehouse]] functions<ref>{{cite magazine |last=Krill |first=Paul |date=November 20, 2003 |title=PostgreSQL boosts open source database |url=https://www.infoworld.com/article/2670451/database/postgresql-boosts-open-source-database.html |magazine=[[InfoWorld]] |access-date=October 21, 2016}}</ref>
|-
! scope="row" | 8.0
| 2005-01-19
| {{Version |o |8.0.26 |style=text-align:center}}
| 2010-10-04
| 2010-10-01
| Native server on [[Microsoft Windows]], [[savepoint]]s, [[tablespace]]s, [[point-in-time recovery]]<ref>{{cite magazine |last=Krill |first=Paul |date=January 19, 2005 |title=PostgreSQL open source database boasts Windows boost |url=https://www.infoworld.com/article/2668622/operating-systems/postgresql-open-source-database-boasts-windows-boost.html |magazine=[[InfoWorld]] |access-date=November 2, 2016}}</ref>
|-
! scope="row" | 8.1
| 2005-11-08
| {{Version |o |8.1.23 |style=text-align:center}}
| 2010-12-16
| 2010-11-08
| Performance optimization, two-phase commit, table [[Partition (database)|partitioning]], index bitmap scan, shared row locking, roles
|-
! scope="row" | 8.2
| 2006-12-05
| {{Version |o |8.2.23 |style=text-align:center}}
| 2011-12-05
| 2011-12-05
| Performance optimization, online index builds, advisory locks, warm standby<ref>{{cite magazine |last=Weiss |first=Todd R. |date=December 5, 2006 |title=Version 8.2 of open-source PostgreSQL DB released |url=https://www.computerworld.com/article/2548483 |magazine=[[Computerworld]] |access-date=October 17, 2016}}</ref>
|-
! scope="row" | 8.3
| 2008-02-04
| {{Version |o |8.3.23 |style=text-align:center}}
| 2013-02-07
| 2013-02-07
| Heap-only tuples, [[full text search]],<ref>{{cite magazine |last=Gilbertson |first=Scott |date=February 5, 2008 |title=PostgreSQL 8.3: Open Source Database Promises Blazing Speed |url=https://www.wired.com/2008/02/postgresql_8dot3_open_source_database_promises_blazing_speed/ |magazine=[[Wired (magazine)|Wired]] |access-date=October 17, 2016}}</ref> [[SQL/XML]], ENUM types, [[Universally unique identifier|UUID]] types
|-
! scope="row" | 8.4
| 2009-07-01
| {{Version |o |8.4.22 |style=text-align:center}}
| 2014-07-24
| 2014-07-24
| [[Window_function_%28SQL%29|Window functions]], column-level permissions, parallel database restore, per-database collation, [[common table expressions]] and recursive queries<ref>{{cite magazine |last=Huber |first=Mathias |date=July 2, 2009 |title=PostgreSQL 8.4 Proves Feature-Rich |url=https://www.linux-magazine.com/Online/News/PostgreSQL-8.4-Proves-Feature-Rich/(language)/eng-US |magazine=[[Linux Magazine]] |access-date=October 17, 2016}}</ref>
|-
! scope="row" | 9.0
| 2010-09-20
| {{Version |o |9.0.23 |style=text-align:center}}
| 2015-10-08
| 2015-10-08
| Built-in binary streaming [[Replication (computing)|replication]], [[hot standby]], in-place upgrade ability, 64-bit Windows<ref>{{cite web |url=https://www.linux.com/news/five-enterprise-features-postgresql-9 |title=Five Enterprise Features in PostgreSQL 9 |last=Brockmeier |first=Joe |date=September 30, 2010 |website=[[Linux.com]] |publisher=[[Linux Foundation]] |access-date=February 6, 2017}}</ref>
|-
! scope="row" | 9.1
| 2011-09-12
| {{Version |o |9.1.24 |style=text-align:center}}
| 2016-10-27
| 2016-10-27
| [[Synchronous replication]], per-column [[collation]]s, unlogged tables, [[serializable snapshot isolation]], writeable common table expressions, [[Security-Enhanced Linux|SELinux]] integration, extensions, foreign tables<ref>{{cite magazine |author=Timothy Prickett Morgan |date=September 12, 2011 |title=PostgreSQL revs to 9.1, aims for enterprise |url=https://www.theregister.co.uk/2011/09/12/postgresql_9_1_cloud_server/ |magazine=[[The Register]] |access-date=February 6, 2017}}</ref>
|-
! scope="row" | 9.2
| 2012-09-10<ref>{{Cite web |url=https://www.postgresql.org/about/news/1415/ |title=PostgreSQL: PostgreSQL 9.2 released |website=www.postgresql.org|date=September 10, 2012 }}</ref>
| {{Version |o |9.2.24 |style=text-align:center}}
| 2017-11-09
| 2017-11-09
| Cascading streaming replication, index-only scans, native [[JSON]] support, improved lock management, range types, pg_receivexlog tool, space-partitioned GiST indexes
|-
! scope="row" | 9.3
| 2013-09-09
| {{Version |o |9.3.25 |style=text-align:center}}
| 2018-11-08
| 2018-11-08
| Custom background workers, data checksums, dedicated JSON operators, LATERAL JOIN, faster pg_dump, new pg_isready server monitoring tool, trigger features, view features, writeable foreign tables, [[materialized view]]s, replication improvements
|-
! scope="row" | 9.4
| 2014-12-18
| {{Version |o |9.4.26 |style=text-align:center}}
| 2020-02-13
| 2020-02-13
| JSONB data type, ALTER SYSTEM statement for changing config values, ability to refresh materialized views without blocking reads, dynamic registration/start/stop of background worker processes, Logical Decoding API, GiN index improvements, Linux huge page support, database cache reloading via pg_prewarm, reintroducing Hstore as the column type of choice for document-style data.<ref>{{Cite web |url=https://www.infoq.com/news/2013/11/Nested-Hstore |title=Reintroducing Hstore for PostgreSQL |website=InfoQ}}</ref>
|-
! scope="row" | 9.5
| 2016-01-07
| {{Version |o |9.5.25 |style=text-align:center}}
| 2021-02-11
| 2021-02-11
| UPSERT, row level security, TABLESAMPLE, CUBE/ROLLUP, GROUPING SETS, and new [[Block Range Index|BRIN]] index<ref>{{cite magazine |last=Richard |first=Chirgwin |date=January 7, 2016 |title=Say oops, UPSERT your head: PostgreSQL version 9.5 has landed |url=https://www.theregister.co.uk/2016/01/07/postgresql_95_lands/ |magazine=[[The Register]] |access-date=October 17, 2016}}</ref>
|-
! scope="row" | 9.6
| 2016-09-29
| {{Version |o |9.6.24 |style=text-align:center}}
| 2021-11-11
| 2021-11-11
| Parallel query support, PostgreSQL foreign data wrapper (FDW) improvements with sort/join pushdown, multiple synchronous standbys, faster vacuuming of large table
|-
! scope="row" | 10
| 2017-10-05
| {{Version |o |10.23 |style=text-align:center}}
| 2022-11-10
| 2022-11-10
| Logical replication,<ref>{{Cite web |url=https://www.postgresql.org/docs/10/logical-replication.html |title=PostgreSQL: Documentation: 10: Chapter&nbsp;31.&nbsp;Logical Replication |website=www.postgresql.org|date=August 12, 2021 }}</ref> declarative table partitioning, improved query parallelism
|-
! scope="row" | 11
| 2018-10-18
| {{Version |o |11.22 |style=text-align:center}}
| 2023-11-09
| 2023-11-09
| Increased robustness and performance for partitioning, transactions supported in stored procedures, enhanced abilities for query parallelism, just-in-time (JIT) compiling for expressions<ref>{{cite web |title=PostgreSQL 11 Released |date=October 18, 2018 |url=https://www.postgresql.org/about/news/1894/ |access-date=October 18, 2018}}</ref><ref>{{cite web |title=PostgreSQLRelease Notes |url=https://www.postgresql.org/docs/11/static/release-11.html |access-date=October 18, 2018}}</ref>
|-
! scope="row" | 12
| 2019-10-03
| {{Version |co |12.19 |style=text-align:center}}
| 2024-05-09
| 2024-11-14
| Improvements to query performance and space utilization; SQL/JSON path expression support; generated columns; improvements to internationalization, and authentication; new pluggable table storage interface.<ref>{{Cite news|url=https://www.postgresql.org/about/news/1976/|title=PostgreSQL: PostgreSQL 12 Released!|newspaper=Postgresql News|date=October 3, 2019}}</ref>
|-
! scope="row" | 13
| 2020-09-24
| {{Version |co |13.15 |style=text-align:center}}
| 2024-05-09
| 2025-11-13
| Space savings and performance gains from de-duplication of B-tree index entries, improved performance for queries that use aggregates or partitioned tables, better query planning when using extended statistics, parallelized vacuuming of indexes, incremental sorting<ref>{{Cite web|url=https://www.postgresql.org/docs/13/release-13.html|title=PostgreSQL 13 Release Notes|website=www.postgresql.org|date=August 12, 2021}}</ref><ref>{{Cite web|url=https://www.postgresql.org/about/news/postgresql-13-released-2077/|title=PostgreSQL 13 Released!|website=www.postgresql.org|date=September 24, 2020}}</ref>
|-
! scope="row" | 14
| 2021-09-30
| {{Version |co |14.12 |style=text-align:center; white-space:nowrap}}
| 2024-05-09
| 2026-11-12
| Added SQL-standard SEARCH and CYCLE clauses for common table expressions, allow DISTINCT to be added to GROUP BY<ref>{{Cite web|url=https://www.postgresql.org/docs/14/release-14.html|title=PostgreSQL 14 Release Notes|website=www.postgresql.org|date=November 11, 2021}}</ref><ref>{{Cite web|url=https://www.postgresql.org/about/news/postgresql-14-released-2318/|title=PostgreSQL 14 Released!|website=www.postgresql.org|date=September 30, 2021}}</ref>
|-
! scope="row" | 15
| 2022-10-13
| {{Version |co |15.7 |style=text-align:center}}
| 2024-05-09
| 2027-11-11
| Implements SQL-standard [[Merge (SQL)|MERGE]] statement. PL/Python now only supports current {{nowrap|Python 3}}, and {{code|plpythonu}} now means {{nowrap|Python 3}}, no longer the discontinued {{nowrap|Python 2}}.
|-
! scope="row" | 16
| 2023-09-14
| {{Version |c |16.3 |style=text-align:center; white-space:nowrap}}
| 2024-05-09
| 2028-11-09
| Improvements to logical replication, pg_stat_io view (for I/O metrics)<ref>{{cite web | url=https://www.postgresql.org/about/news/postgresql-16-released-2715/ | title=PostgreSQL 16 Released! | date=September 14, 2023 }}</ref>
|-
! scope="row" | 17
| {{sdash}}
| {{Version |p |17.0 |style=text-align:center; white-space:nowrap}}
| 2024-05-23
| {{sdash}}
| <!-- TODO, or wait until release -->
|}
{{Version |l |show=111111}}
{{Timeline PostgreSQL}}

== See also ==
{{Portal|Free and open-source software}}

* [[Comparison of relational database management systems]]
* [[Database scalability]]
* [[List of databases using MVCC]]
* [[LLVM]] (llvmjit is the JIT engine used by PostgreSQL)

== References ==
{{reflist|refs=
<ref name="birthday">{{cite web |url=https://www.postgresql.org/about/news/978/ |title=Happy Birthday, PostgreSQL! |date=July 8, 2008 |publisher=PostgreSQL Global Development Group}}</ref>
<ref name="approved by OSI">{{cite web |date=February 18, 2010 |title=PostgreSQL licence approved by OSI |url=http://www.crynwr.com/cgi-bin/ezmlm-cgi?17:mmp:969 |publisher=Crynwr |access-date=February 18, 2010 |archive-url=https://web.archive.org/web/20160808093031/http://www.crynwr.com/cgi-bin/ezmlm-cgi?17:mmp:969 |archive-date=August 8, 2016 |url-status=dead}}</ref>
<ref name="OSI">{{cite web |publisher=Open Source Initiative |date=February 20, 2010 |title=OSI PostgreSQL Licence |url=https://www.opensource.org/licenses/postgresql |access-date=February 20, 2010}}</ref>
<ref name="about/licence">{{cite web |url=https://www.postgresql.org/about/licence |title=License |publisher=PostgreSQL Global Development Group |access-date=September 20, 2010}}</ref>
<ref name="intro-whatis">{{cite web |url=https://www.postgresql.org/docs/current/static/intro-whatis.html |title=What is PostgreSQL? |work=PostgreSQL 9.3.0 Documentation |publisher=PostgreSQL Global Development Group |access-date=September 20, 2013}}</ref>

<!-- <ref name="OS X Lion Server">{{cite web |date=August 4, 2011 |title=OS X Lion Server&nbsp;— Technical Specifications |url=http://support.apple.com/kb/SP630 | quote=Web Hosting [..] PostgreSQL |access-date=November 12, 2011}}</ref> -->
<ref name="contributors">{{cite web |url=https://www.postgresql.org/community/contributors/ |title=Contributor Profiles |publisher=PostgreSQL Global Development Group |access-date=March 14, 2017}}</ref>

<ref name="Audio sample">{{Cite web|url=https://www.postgresql.org/files/postgresql.mp3|title=Audio sample, 5.6k MP3}}</ref>
<ref name="Project name">{{cite web |date=November 16, 2007 |title=Project name – statement from the core team |publisher=archives.postgresql.org |url=http://archives.postgresql.org/pgsql-advocacy/2007-11/msg00109.php |access-date=November 16, 2007}}</ref>
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<ref name="about/history">{{cite web |url=https://www.postgresql.org/about/history/ |title=PostgreSQL: History |publisher=PostgreSQL Global Development Group |access-date=August 27, 2016 |archive-url=https://web.archive.org/web/20170326020245/https://www.postgresql.org/about/history/ |archive-date=March 26, 2017 |url-status=dead}}</ref>
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<ref name="pavel-history">{{cite web |author=Pavel Stehule |date=9 June 2012 |title=Historie projektu PostgreSQL |language=cs |url=http://postgres.cz/wiki/Historie_projektu_PostgreSQL}}</ref>
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<ref name="20th anniversary">{{cite mailing list |url=https://www.postgresql.org/message-id/CA+OCxozS_cuaLw=nfS=GdJZmS7ygjhdtZbqVt17wPLfCOtFY4g@mail.gmail.com |title=Re: 20th anniversary of PostgreSQL ? |date=April 7, 2015 |access-date=April 9, 2015 |mailing-list=pgsql-advocacy |last=Page |first=Dave}}</ref>
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<ref name="H Online">{{citation |publisher=H Online |url=http://www.h-online.com/open/news/item/PostgreSQL-9-1-with-synchronous-replication-1341228.html |type=news |title=PostgreSQL 9.1 with synchronous replication}}</ref>
<ref name="SP-GiST">{{cite conference |last1=Bartunov |first1=O |last2=Sigaev |first2=T |date=May 2011 |title=SP-GiST – a new indexing framework for PostgreSQL |conference=PGCon 2011 |location=Ottawa, Canada |url=http://www.pgcon.org/2011/schedule/attachments/197_pgcon-2011.pdf |access-date=January 31, 2016}}</ref>
<ref name="KNN-GiST">{{cite conference |last1=Bartunov |first1=O |last2=Sigaev |first2=T |date=May 2010 |title=K-nearest neighbour search for PostgreSQL |conference=PGCon 2010 |location=Ottawa, Canada |url=http://www.pgcon.org/2010/schedule/attachments/168_pgcon-2010-1.pdf |access-date=January 31, 2016}}</ref>
<ref name="Postgres-XC">{{cite web |publisher=Postgres-XC |url=http://postgres-xc.sourceforge.net/ |type=website |title=Postgres-XC project page |url-status=dead |archive-url=https://web.archive.org/web/20120701122448/http://postgres-xc.sourceforge.net/ |archive-date=July 1, 2012 |df=mdy-all}}</ref>
<ref name="Fischer">{{cite press release |author=Marit Fischer |date=November 10, 2007 |title=Backcountry.com finally gives something back to the open source community |publisher=Backcountry.com |url=http://www.backcountrycorp.com/corporate/section/3/press/a511/Backcountry-finally-gives-something-back-to-the-open-source-community.html |url-status=dead |archive-url=https://web.archive.org/web/20101226124550/http://www.backcountrycorp.com/corporate/section/3/press/a511/Backcountry-finally-gives-something-back-to-the-open-source-community.html |archive-date=December 26, 2010 |df=mdy-all}}</ref>
<ref name="jsonb">{{cite web |first=Peter |last=Geoghegan |date=March 23, 2014 |title=What I think of jsonb |url=http://pgeoghegan.blogspot.com/2014/03/what-i-think-of-jsonb.html}}</ref>
<ref name="psycopg2">{{cite web |url=http://initd.org/psycopg/ |title=PostgreSQL + Python &#124; Psycopg |work=initd.org}}</ref>
<ref name="materialized_views">{{cite web |date=March 4, 2013 |title=Add a materialized view relations |url=https://www.postgresql.org/message-id/E1UCJDN-00042x-0w@gemulon.postgresql.org |access-date=March 4, 2013}}</ref>
<ref name="updatable_views">{{cite web |date=December 8, 2012 |title=Support automatically-updatable views |url=http://archives.postgresql.org/pgsql-committers/2012-12/msg00154.php |access-date=December 8, 2012}}</ref>
<ref name="recursive_views">{{cite web |date=February 1, 2013 |title=Add CREATE RECURSIVE VIEW syntax |url=https://www.postgresql.org/message-id/E1U17NB-0006c6-DX@gemulon.postgresql.org |access-date=February 28, 2013}}</ref>
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<ref name="Bernier">{{cite web |url=http://www.oreillynet.com/pub/a/databases/2006/02/02/postgresq_regexes.html |title=Using Regular Expressions in PostgreSQL |last=Bernier |first=Robert |publisher=[[O'Reilly Media]] |date=February 2, 2006 |access-date=September 25, 2010}}</ref>
<ref name="POODLE">{{cite web |url=http://blog.hagander.net/archives/222-A-few-short-notes-about-PostgreSQL-and-POODLE.html |title=A few short notes about PostgreSQL and POODLE |work=hagander.net}}</ref>
<ref name="Berkus">{{cite web |last=Berkus |first=Josh |date=July 6, 2007 |title=PostgreSQL publishes first real benchmark |url=http://blogs.ittoolbox.com/database/soup/archives/postgresql-publishes-first-real-benchmark-17470 |access-date=July 10, 2007 |archive-url=https://web.archive.org/web/20070712092901/http://blogs.ittoolbox.com/database/soup/archives/postgresql-publishes-first-real-benchmark-17470 |archive-date=July 12, 2007 |url-status=dead |df=mdy-all}}</ref>
<ref name="Vilmos">{{cite web |last=Vilmos |first=György |date=September 29, 2009 |title=PostgreSQL history |url=http://suckit.blog.hu/2009/09/29/postgresql_history |access-date=August 28, 2010}}</ref>
<ref name="SPECJ">{{cite web |publisher=[[SPEC]] |date=July 6, 2007 |title=SPECjAppServer2004 Result |url=http://www.spec.org/jAppServer2004/results/res2007q3/jAppServer2004-20070606-00065.html |access-date=July 10, 2007}}</ref>
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<ref name="MusicBrainz">{{cite web |url=http://musicbrainz.org/doc/Database |title=Database – MusicBrainz |publisher=MusicBrainz Wiki |access-date=February 5, 2011}}</ref>
<ref name="ISS">{{cite web |date=July 13, 2010 |author=Duncavage, Daniel P |title=NASA needs Postgres-Nagios help |url=http://archives.postgresql.org/pgsql-general/2010-07/msg00394.php}}</ref>
<ref name="MyYearbook">{{cite web |author=Roy, Gavin M |title=PostgreSQL at myYearbook.com |location=USA East |year=2010 |type=talk |url=https://www.postgresqlconference.org/2010/east/talks/postgresql_at_myyearbook.com |publisher=PostgreSQL Conference |url-status=dead |archive-url=https://web.archive.org/web/20110727183016/https://www.postgresqlconference.org/2010/east/talks/postgresql_at_myyearbook.com |archive-date=July 27, 2011 |df=mdy-all}}</ref>
<ref name="Instagram">{{cite web |url=http://instagram-engineering.tumblr.com/post/20541814340/keeping-instagram-up-with-over-a-million-new-users-in#replicationread-slaves |title=Keeping Instagram up with over a million new users in twelve hours |publisher=Instagram-engineering.tumblr.com |date=May 17, 2011 |access-date=July 7, 2012}}</ref>
<ref name="Disqus">{{cite web |url=https://speakerdeck.com/mikeclarke/pgcon-2013-keynote-postgres-at-disqus |title=Postgres at Disqus |access-date=May 24, 2013}}</ref>
<ref name="TripAdvisor">{{cite conference |url=http://www.pgconf.us/2015/event/95/ |title=At the Heart of a Giant: Postgres at TripAdvisor |last=Kelly |first=Matthew |date=March 27, 2015 |conference=PGConf US 2015 |access-date=July 23, 2015 |archive-url=https://web.archive.org/web/20150723181100/http://www.pgconf.us/2015/event/95/ |archive-date=July 23, 2015 |url-status=dead}} ([https://www.youtube.com/watch?v=YquXmwZNnfg Presentation video])</ref>
<ref name="Heroku">{{cite news |date=1 April 2013 |author=Alex Williams |title=Heroku Forces Customer Upgrade To Fix Critical PostgreSQL Security Hole |work=TechCrunch |url=https://techcrunch.com/2013/04/01/heroku-forces-customer-upgrade-to-fix-critical-postgresql-security-hole/}}</ref>
<ref name="Darrow">{{cite news |date=11 November 2013 |author=Barb Darrow |title=Heroku gussies up Postgres with database roll-back and proactive alerts |url=http://gigaom.com/2013/11/11/heroku-gussies-up-postgres-with-database-roll-back-and-proactive-alerts/ |publisher=GigaOM}}</ref>
<ref name="Kerstiens">{{cite web |date=26 September 2013 |author=Craig Kerstiens |title=WAL-E and Continuous Protection with Heroku Postgres |publisher=Heroku blog |url=https://blog.heroku.com/archives/2013/9/26/wal_e_and_continuous_protection_with_heroku_postgres}}</ref>
<ref name="Techweekeurope">{{cite web |url=http://www.techweekeurope.co.uk/news/enterprisedb-offers-up-postgres-plus-cloud-database-57030 |title=EnterpriseDB Offers Up Postgres Plus Cloud Database |publisher=Techweekeurope.co.uk |date=January 27, 2012 |access-date=July 7, 2012}}</ref>
<ref name="Sargent">{{cite news |date=15 May 2012 |author=Al Sargent |title=Introducing VMware vFabric Suite 5.1: Automated Deployment, New Components, and Open Source Support |url=https://blogs.vmware.com/vfabric/2012/05/announcing-vmware-vfabric-suite-51.html |publisher=VMware blogs}}</ref>
<ref name="aws.typepad.com">{{cite news |date=14 November 2013 |author=Jeff |title=Amazon RDS for PostgreSQL – Now Available |publisher=Amazon Web Services Blog |url=http://aws.typepad.com/aws/2013/11/amazon-rds-for-postgresql-now-available.html}}</ref>
<ref name="Williams">{{cite news |date=14 November 2013 |author=Alex Williams |title=PostgreSQL Now Available On Amazon's Relational Database Service |work=TechCrunch |url=https://techcrunch.com/2013/11/14/postgressql-now-available-on-amazons-relational-database-service/}}</ref>
<ref name="postgres-r">{{cite web |url=http://www.postgres-r.org/ |title=Postgres-R: a database replication system for PostgreSQL |publisher=Postgres Global Development Group |access-date=August 27, 2016 |archive-url=https://web.archive.org/web/20100329215559/http://www.postgres-r.org/ |archive-date=March 29, 2010 |url-status=dead}}</ref>
<ref name="bdr">{{cite web |url=http://2ndquadrant.com/en/resources/bdr/ |title=Postgres-BDR |publisher=2ndQuadrant Ltd |access-date=August 27, 2016}}</ref>
<ref name="raspi">{{cite web |url=http://raspberrypg.org/2015/06/step-5-update-installing-postgresql-on-my-raspberry-pi-1-and-2/ |title=Step 5 (update): Installing PostgreSQL on my Raspberry Pi 1 and 2 |first=Rubens |last=Souza |date=June 17, 2015 |access-date=August 27, 2016 |website=Raspberry PG}}</ref>
<ref name="Auto-Replication">{{cite web |url=https://dzone.com/articles/asynchronous-master-slave-replication-of-postgresq |title=Asynchronous Master-Slave Replication of PostgreSQL Databases in One Click |publisher=DZone |access-date=May 26, 2017}}</ref>
<ref name="identifiers">{{cite web |url=https://www.postgresql.org/docs/current/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS |title=Case sensitivity of identifiers |date=November 11, 2021 |publisher=PostgreSQL Global Development Group}}</ref>
<ref name="OS X">{{cite web |url=https://www.postgresql.org/download/macosx/ |title=Mac OS X packages |publisher=The PostgreSQL Global Development Group |access-date=August 27, 2016}}</ref>
}}


== Further reading ==
=== Performance tuning documentation ===
{{Refbegin}}
*[http://www.revsys.com/writings/postgresql-performance.html PostgreSQL Performance Tuning]
* {{cite book |title=PostgreSQL: Up and Running |first1=Regina |last1=Obe |first2=Leo |last2=Hsu |date=July 8, 2012 |publisher=[[O'Reilly Media|O'Reilly]] |isbn=978-1-4493-2633-3 |url=http://www.postgresonline.com/store.php?asin=1449326331}}
*[http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html Tuning PostgreSQL for performance]
* {{cite book |title=PostgreSQL Server Programming |edition=second |first1=Hannu |last1=Krosing |first2=Kirk |last2=Roybal |date=June 15, 2013 |publisher=[[Packt Publishing]] |isbn=978-1-84951-698-3 |url=http://www.2ndquadrant.com/books/}}
*[http://www.powerpostgresql.com/Downloads/annotated_conf_80.html Annotated POSTGRESQL.CONF Guide for PostgreSQL]
* {{cite book |title=PostgreSQL 9 Administration Cookbook |edition=second |first1=Simon |last1=Riggs |first2=Hannu |last2=Krosing |date=October 27, 2010 |publisher=[[Packt Publishing]] |isbn=978-1-84951-028-8 |url=http://www.2ndquadrant.com/books/}}
* {{cite book |title=PostgreSQL 9 High Performance |first=Greg |last=Smith |date=October 15, 2010 |publisher=[[Packt Publishing]] |isbn=978-1-84951-030-1 |url=http://www.2ndquadrant.com/books/}}
* {{cite book |title=Beginning PHP and PostgreSQL 8: From Novice to Professional |first1=W. Jason |last1=Gilmore |first2=Robert |last2=Treat |date=February 27, 2006 |publisher=[[Apress]] |isbn=1-59059-547-5 |url=http://www.apress.com/book/view/1590595475 |pages=896 |access-date=April 28, 2009 |archive-url=https://web.archive.org/web/20090708113944/http://www.apress.com/book/view/1590595475 |archive-date=July 8, 2009 |url-status=dead |df=mdy-all}}
* {{cite book |title=PostgreSQL |edition=second |first=Korry |last=Douglas |date=August 5, 2005 |publisher=[[Sams Publishing|Sams]] |isbn=0-672-32756-2 |url=http://www.informit.com/store/product.aspx?isbn=0672327562 |pages=1032}}
* {{cite book |title=Beginning Databases with PostgreSQL |edition=second |first1=Neil |last1=Matthew |first2=Richard |last2=Stones |date=April 6, 2005 |publisher=[[Apress]] |isbn=1-59059-478-9 |url=http://www.apress.com/book/view/9781590594780 |pages=664 |access-date=April 28, 2009 |archive-url=https://web.archive.org/web/20090409150911/http://www.apress.com/book/view/9781590594780 |archive-date=April 9, 2009 |url-status=dead |df=mdy-all}}
* {{cite book |title=Practical PostgreSQL |first1=John C. |last1=Worsley |first2=Joshua D. |last2=Drake |date=January 2002 |publisher=[[O'Reilly Media]] |isbn=1-56592-846-6 |url=https://archive.org/details/practicalpostgre00wors/page/636 |pages=[https://archive.org/details/practicalpostgre00wors/page/636 636<!-- link says 640 pages, but "pp=" is to cite a "range of pages in the source that support the content (not an indication of the number of pages in the source)" and "p=" for a single one.. not sure page 636 (and similar for books above) is done here to cite anything special, at least then not changing here for now.-->] |url-access=registration }}
{{Refend}}


== External links ==
{{Databases}}
{{Commons category}}
{{Wikibooks|PostgreSQL}}
* {{Official website}}, and [https://wiki.postgresql.org/ wiki]
* A [https://www.postgresql.org/download/product-categories/ Software Catalog] of related projects and products
* The official [https://git.postgresql.org/gitweb/?p=postgresql.git Main Source Code Repository (for browsing)], and the [https://wiki.postgresql.org/wiki/Developer_FAQ Developer FAQ]
* The official [https://www.postgresql.org/docs/current/docguide.html Reference for PostgreSQL Documentation Authors]
* All official [https://git.postgresql.org/ PostgreSQL Source Code Repositories]
* {{Curlie|Computers/Software/Databases/PostgreSQL}}
* {{GitHub|postgres|PostgreSQL}}


{{Software in the Public Interest}}
[[Category:Database management systems]]
{{Authority control}}
[[Category:Open source database management systems]]


[[ca:PostgreSQL]]
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[[Category:Cross-platform software]]
[[da:PostgreSQL]]
[[Category:Free database management systems]]
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[[Category:Free software programmed in C]]
[[es:PostgreSQL]]
[[Category:ORDBMS software for Linux]]
[[eu:PostgreSQL]]
[[Category:Relational database management software for Linux]]
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[[Category:Software that uses Meson]]
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Latest revision as of 02:09, 29 May 2024

PostgreSQL
Developer(s)PostgreSQL Global Development Group[2]
Initial release8 July 1996;
27 years ago
 (1996-07-08)[3]
Stable release
16.3[4] Edit this on Wikidata / 9 May 2024; 22 days ago (9 May 2024)
Preview release
17 Beta 1 / 23 May 2024;
8 days ago
 (2024-05-23)[5]
Repository
Written inC
TypeRDBMS
LicensePostgreSQL License (free and open-source, permissive)[6][7][8]
Websitewww.postgresql.org Edit this on Wikidata
PostgreSQL License[6]
PublisherPostgreSQL Global Development Group
Regents of the University of California
Debian FSG compatibleYes[9][10]
FSF approvedYes[11]
OSI approvedYes[8]
GPL compatibleYes
CopyleftNo
Linking from code with a different licenceYes
Websitepostgresql.org/about/licence

PostgreSQL (/ˈpstɡrɛs ˌkjuː ˈɛl/, POHST-gres kyoo el),[12][13] also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. PostgreSQL features transactions with atomicity, consistency, isolation, durability (ACID) properties, automatically updatable views, materialized views, triggers, foreign keys, and stored procedures.[14] It is supported on all major operating systems, including Linux, FreeBSD, OpenBSD, macOS, and Windows, and handles a range of workloads from single machines to data warehouses or web services with many concurrent users.

The PostgreSQL Global Development Group focuses only on developing a database engine and closely related components. This core is, technically, what comprises PostgreSQL itself, but there is an extensive developer community and ecosystem that provides other important feature sets that might, traditionally, be provided by a proprietary software vendor. These include special-purpose database engine features, like those needed to support a geospatial[15] or temporal[16] database or features which emulate other database products.[17][18][19][20] Also available from third parties are a wide variety of user and machine interface features, such as graphical user interfaces[21][22][23] or load balancing and high availability toolsets.[24] The large third-party PostgreSQL support network of people, companies, products, and projects, even though not part of The PostgreSQL Development Group, are essential to the PostgreSQL database engine's adoption and use and make up the PostgreSQL ecosystem writ large.[25]

PostgreSQL was originally named POSTGRES, referring to its origins as a successor to the Ingres database developed at the University of California, Berkeley.[26][27] In 1996, the project was renamed PostgreSQL to reflect its support for SQL. After a review in 2007, the development team decided to keep the name PostgreSQL and the alias Postgres.[28]

History[edit]

PostgreSQL evolved from the Ingres project at the University of California, Berkeley. In 1982, the leader of the Ingres team, Michael Stonebraker, left Berkeley to make a proprietary version of Ingres.[26] He returned to Berkeley in 1985, and began a post-Ingres project to address the problems with contemporary database systems that had become increasingly clear during the early 1980s. He won the Turing Award in 2014 for these and other projects,[29] and techniques pioneered in them.

The new project, POSTGRES, aimed to add the fewest features needed to completely support data types.[30] These features included the ability to define types and to fully describe relationships – something used widely, but maintained entirely by the user. In POSTGRES, the database understood relationships, and could retrieve information in related tables in a natural way using rules. POSTGRES used many of the ideas of Ingres, but not its code.[31]

Starting in 1986, published papers described the basis of the system, and a prototype version was shown at the 1988 ACM SIGMOD Conference. The team released version 1 to a small number of users in June 1989, followed by version 2 with a re-written rules system in June 1990. Version 3, released in 1991, again re-wrote the rules system, and added support for multiple storage managers[32] and an improved query engine. By 1993, the number of users began to overwhelm the project with requests for support and features. After releasing version 4.2[33] on June 30, 1994 – primarily a cleanup – the project ended. Berkeley released POSTGRES under an MIT License variant, which enabled other developers to use the code for any use. At the time, POSTGRES used an Ingres-influenced POSTQUEL query language interpreter, which could be interactively used with a console application named monitor.

In 1994, Berkeley graduate students Andrew Yu and Jolly Chen replaced the POSTQUEL query language interpreter with one for the SQL query language, creating Postgres95. The monitor console was also replaced by psql. Yu and Chen announced the first version (0.01) to beta testers on May 5, 1995. Version 1.0 of Postgres95 was announced on September 5, 1995, with a more liberal license that enabled the software to be freely modifiable.

On July 8, 1996, Marc Fournier at Hub.org Networking Services provided the first non-university development server for the open-source development effort.[3] With the participation of Bruce Momjian and Vadim B. Mikheev, work began to stabilize the code inherited from Berkeley.

In 1996, the project was renamed to PostgreSQL to reflect its support for SQL. The online presence at the website PostgreSQL.org began on October 22, 1996.[34] The first PostgreSQL release formed version 6.0 on January 29, 1997. Since then developers and volunteers around the world have maintained the software as The PostgreSQL Global Development Group.[2]

The project continues to make releases available under its free and open-source software PostgreSQL License. Code comes from contributions from proprietary vendors, support companies, and open-source programmers.

Multiversion concurrency control (MVCC)[edit]

PostgreSQL manages concurrency through multiversion concurrency control (MVCC), which gives each transaction a "snapshot" of the database, allowing changes to be made without affecting other transactions. This largely eliminates the need for read locks, and ensures the database maintains ACID principles. PostgreSQL offers four levels of transaction isolation: Read Uncommitted, Read Committed, Repeatable Read and Serializable. Because PostgreSQL is immune to dirty reads, requesting a Read Uncommitted transaction isolation level provides read committed instead. PostgreSQL supports full serializability via the serializable snapshot isolation (SSI) method.[35] The PostreSQL MVCC implementation is prone to performance issues that require tuning when under a heavy write load which updates existing rows.[36]

Storage and replication[edit]

Replication[edit]

PostgreSQL includes built-in binary replication based on shipping the changes (write-ahead logs (WAL)) to replica nodes asynchronously, with the ability to run read-only queries against these replicated nodes. This allows splitting read traffic among multiple nodes efficiently. Earlier replication software that allowed similar read scaling normally relied on adding replication triggers to the master, increasing load.

PostgreSQL includes built-in synchronous replication[37] that ensures that, for each write transaction, the master waits until at least one replica node has written the data to its transaction log. Unlike other database systems, the durability of a transaction (whether it is asynchronous or synchronous) can be specified per-database, per-user, per-session or even per-transaction. This can be useful for workloads that do not require such guarantees, and may not be wanted for all data as it slows down performance due to the requirement of the confirmation of the transaction reaching the synchronous standby.

Standby servers can be synchronous or asynchronous. Synchronous standby servers can be specified in the configuration which determines which servers are candidates for synchronous replication. The first in the list that is actively streaming will be used as the current synchronous server. When this fails, the system fails over to the next in line.

Synchronous multi-master replication is not included in the PostgreSQL core. Postgres-XC which is based on PostgreSQL provides scalable synchronous multi-master replication.[38] It is licensed under the same license as PostgreSQL. A related project is called Postgres-XL. Postgres-R is yet another fork.[39] Bidirectional replication (BDR) is an asynchronous multi-master replication system for PostgreSQL.[40]

Tools such as repmgr make managing replication clusters easier.

Several asynchronous trigger-based replication packages are available. These remain useful even after introduction of the expanded core abilities, for situations where binary replication of a full database cluster is inappropriate:

Indexes[edit]

PostgreSQL includes built-in support for regular B-tree and hash table indexes, and four index access methods: generalized search trees (GiST), generalized inverted indexes (GIN), Space-Partitioned GiST (SP-GiST)[42] and Block Range Indexes (BRIN). In addition, user-defined index methods can be created, although this is quite an involved process. Indexes in PostgreSQL also support the following features:

  • Expression indexes can be created with an index of the result of an expression or function, instead of simply the value of a column.
  • Partial indexes, which only index part of a table, can be created by adding a WHERE clause to the end of the CREATE INDEX statement. This allows a smaller index to be created.
  • The planner is able to use multiple indexes together to satisfy complex queries, using temporary in-memory bitmap index operations (useful for data warehouse applications for joining a large fact table to smaller dimension tables such as those arranged in a star schema).
  • k-nearest neighbors (k-NN) indexing (also referred to KNN-GiST[43]) provides efficient searching of "closest values" to that specified, useful to finding similar words, or close objects or locations with geospatial data. This is achieved without exhaustive matching of values.
  • Index-only scans often allow the system to fetch data from indexes without ever having to access the main table.
  • Block Range Indexes (BRIN).

Schemas[edit]

PostgreSQL schemas are namespaces, allowing objects of the same kind and name to co-exist in a single database. They are not to be confused with a database schema -- the abstract, structural, organizational specification which defines how every table's data relates to data within other tables. All PostgreSQL database objects, except for a few global objects such as roles and tablespaces, exist within a schema. They cannot be nested, schemas cannot contain schemas. The permission system controls access to schemas and their content. By default, newly created databases have only a single schema called public but other schemas can be added and the public schema isn't mandatory.

A search_path setting determines the order in which PostgreSQL checks schemas for unqualified objects (those without a prefixed schema). By default, it is set to $user, public ($user refers to the currently connected database user). This default can be set on a database or role level, but as it is a session parameter, it can be freely changed (even multiple times) during a client session, affecting that session only.

Non-existent schemas, or other schemas not accessible to the logged-in user, that are listed in search_path are silently skipped during object lookup.

New objects are created in whichever valid schema (one that can be accessed) appears first in the search_path.

Data types[edit]

A wide variety of native data types are supported, including:

In addition, users can create their own data types which can usually be made fully indexable via PostgreSQL's indexing infrastructures – GiST, GIN, SP-GiST. Examples of these include the geographic information system (GIS) data types from the PostGIS project for PostgreSQL.

There is also a data type called a domain, which is the same as any other data type but with optional constraints defined by the creator of that domain. This means any data entered into a column using the domain will have to conform to whichever constraints were defined as part of the domain.

A data type that represents a range of data can be used which are called range types. These can be discrete ranges (e.g. all integer values 1 to 10) or continuous ranges (e.g., any time between 10:00 am and 11:00 am). The built-in range types available include ranges of integers, big integers, decimal numbers, time stamps (with and without time zone) and dates.

Custom range types can be created to make new types of ranges available, such as IP address ranges using the inet type as a base, or float ranges using the float data type as a base. Range types support inclusive and exclusive range boundaries using the [] and () characters respectively. (e.g., [4,9) represents all integers starting from and including 4 up to but not including 9.) Range types are also compatible with existing operators used to check for overlap, containment, right of etc.

User-defined objects[edit]

New types of almost all objects inside the database can be created, including:

  • Casts
  • Conversions
  • Data types
  • Data domains
  • Functions, including aggregate functions and window functions
  • Indexes including custom indexes for custom types
  • Operators (existing ones can be overloaded)
  • Procedural languages

Inheritance[edit]

Tables can be set to inherit their characteristics from a parent table. Data in child tables will appear to exist in the parent tables, unless data is selected from the parent table using the ONLY keyword, i.e. SELECT * FROM ONLY parent_table;. Adding a column in the parent table will cause that column to appear in the child table.

Inheritance can be used to implement table partitioning, using either triggers or rules to direct inserts to the parent table into the proper child tables.

This feature is not fully supported. In particular, table constraints are not currently inheritable. All check constraints and not-null constraints on a parent table are automatically inherited by its children. Other types of constraints (unique, primary key, and foreign key constraints) are not inherited.

Inheritance provides a way to map the features of generalization hierarchies depicted in entity relationship diagrams (ERDs) directly into the PostgreSQL database.

Other storage features[edit]

  • Referential integrity constraints including foreign key constraints, column constraints, and row checks
  • Binary and textual large-object storage
  • Tablespaces
  • Per-column collation
  • Online backup
  • Point-in-time recovery, implemented using write-ahead logging
  • In-place upgrades with pg_upgrade for less downtime

Control and connectivity[edit]

Foreign data wrappers[edit]

PostgreSQL can link to other systems to retrieve data via foreign data wrappers (FDWs).[46] These can take the form of any data source, such as a file system, another relational database management system (RDBMS), or a web service. This means that regular database queries can use these data sources like regular tables, and even join multiple data-sources together.

Interfaces[edit]

PostgreSQL supports a binary communication protocol that allows applications to connect to the database server. The protocol is versioned (currently 3.0, as of PostgreSQL 7.4) and has a detailed specification.[47]

The official client implementation of this communication protocol is a C API, libpq.[48] In addition, the officially supported ECPG tool allows SQL commands to be embedded in C code.[49] Both are part of the standard PostgreSQL distribution.[50]

Third-party libraries for connecting to PostgreSQL are available for many programming languages, including C++,[51] Java,[52] Julia,[53][54][55] Python,[56] Node.js,[57] Go,[58] and Rust.[59]

Procedural languages[edit]

Procedural languages allow developers to extend the database with custom subroutines (functions), often called stored procedures. These functions can be used to build database triggers (functions invoked on modification of certain data) and custom data types and aggregate functions.[60] Procedural languages can also be invoked without defining a function, using a DO command at SQL level.[61]

Languages are divided into two groups: Procedures written in safe languages are sandboxed and can be safely created and used by any user. Procedures written in unsafe languages can only be created by superusers, because they allow bypassing a database's security restrictions, but can also access sources external to the database. Some languages like Perl provide both safe and unsafe versions.

PostgreSQL has built-in support for three procedural languages:

  • Plain SQL (safe). Simpler SQL functions can get expanded inline into the calling (SQL) query, which saves function call overhead and allows the query optimizer to "see inside" the function.
  • Procedural Language/PostgreSQL (PL/pgSQL) (safe), which resembles Oracle's Procedural Language for SQL (PL/SQL) procedural language and SQL/Persistent Stored Modules (SQL/PSM).
  • C (unsafe), which allows loading one or more custom shared library into the database. Functions written in C offer the best performance, but bugs in code can crash and potentially corrupt the database. Most built-in functions are written in C.

In addition, PostgreSQL allows procedural languages to be loaded into the database through extensions. Three language extensions are included with PostgreSQL to support Perl, Tcl, and Python. For Python, the current Python 3 is used, and the discontinued Python 2 is no longer supported as of PostgreSQL 15. Both were supported previously, defaulting to Python 2, while old and new versions couldn't be used in the same session.[62] External projects provide support for many other languages,[63] including PL/Java, JavaScript (PL/V8), PL/Julia,[55] PL/R,[64] PL/Ruby, and others.

Triggers[edit]

Triggers are events triggered by the action of SQL data manipulation language (DML) statements. For example, an INSERT statement might activate a trigger that checks if the values of the statement are valid. Most triggers are only activated by either INSERT or UPDATE statements.

Triggers are fully supported and can be attached to tables. Triggers can be per-column and conditional, in that UPDATE triggers can target specific columns of a table, and triggers can be told to execute under a set of conditions as specified in the trigger's WHERE clause. Triggers can be attached to views by using the INSTEAD OF condition. Multiple triggers are fired in alphabetical order. In addition to calling functions written in the native PL/pgSQL, triggers can also invoke functions written in other languages like PL/Python or PL/Perl.

Asynchronous notifications[edit]

PostgreSQL provides an asynchronous messaging system that is accessed through the NOTIFY, LISTEN and UNLISTEN commands. A session can issue a NOTIFY command, along with the user-specified channel and an optional payload, to mark a particular event occurring. Other sessions are able to detect these events by issuing a LISTEN command, which can listen to a particular channel. This functionality can be used for a wide variety of purposes, such as letting other sessions know when a table has updated or for separate applications to detect when a particular action has been performed. Such a system prevents the need for continuous polling by applications to see if anything has yet changed, and reducing unnecessary overhead. Notifications are fully transactional, in that messages are not sent until the transaction they were sent from is committed. This eliminates the problem of messages being sent for an action being performed which is then rolled back.

Many connectors for PostgreSQL provide support for this notification system (including libpq, JDBC, Npgsql, psycopg and node.js) so it can be used by external applications.

PostgreSQL can act as an effective, persistent "pub/sub" server or job server by combining LISTEN with FOR UPDATE SKIP LOCKED.[65][66][67]

Rules[edit]

Rules allow the "query tree" of an incoming query to be rewritten; they are an, automatically invoked, macro language for SQL. "Query Re-Write Rules" are attached to a table/class and "Re-Write" the incoming DML (select, insert, update, and/or delete) into one or more queries that either replace the original DML statement or execute in addition to it. Query Re-Write occurs after DML statement parsing and before query planning.

The functionality rules provide was, in almost every way, later duplicated with the introduction of newer types of triggers. The use of triggers is usually preferred over rules as it is easier to reason about trigger behavior and interactions than when equivalent rules are used.

Other querying features[edit]

  • Transactions
  • Full-text search
  • Views
    • Materialized views[68]
    • Updateable views[69]
    • Recursive views[70]
  • Inner, outer (full, left, and right), and cross joins
  • Sub-selects
    • Correlated sub-queries[71]
  • Regular expressions[72]
  • Common table expressions and writable common table expressions
  • Encrypted connections via Transport Layer Security (TLS); current versions do not use vulnerable SSL, even with that configuration option[73]
  • Domains
  • Savepoints
  • Two-phase commit
  • The Oversized-Attribute Storage Technique (TOAST) is used to transparently store large table attributes (such as big MIME attachments or XML messages) in a separate area, with automatic compression.
  • Embedded SQL is implemented using preprocessor. SQL code is first written embedded into C code. Then code is run through ECPG preprocessor, which replaces SQL with calls to code library. Then code can be compiled using a C compiler. Embedding works also with C++ but it does not recognize all C++ constructs.

Concurrency model[edit]

PostgreSQL server is process-based (not threaded), and uses one operating system process per database session. Multiple sessions are automatically spread across all available CPUs by the operating system. Many types of queries can also be parallelized across multiple background worker processes, taking advantage of multiple CPUs or cores.[74] Client applications can use threads and create multiple database connections from each thread.[75]

Security[edit]

PostgreSQL manages its internal security on a per-role basis. A role is generally regarded to be a user (a role that can log in), or a group (a role of which other roles are members). Permissions can be granted or revoked on any object down to the column level, and can allow or prevent the visibility/creation/alteration/deletion of objects at the database, schema, table, and row levels.

PostgreSQL's SECURITY LABEL feature (extension to SQL standards), allows for additional security; with a bundled loadable module that supports label-based mandatory access control (MAC) based on Security-Enhanced Linux (SELinux) security policy.[76][77]

PostgreSQL natively supports a broad number of external authentication mechanisms, including:

The GSSAPI, SSPI, Kerberos, peer, ident and certificate methods can also use a specified "map" file that lists which users matched by that authentication system are allowed to connect as a specific database user.

These methods are specified in the cluster's host-based authentication configuration file (pg_hba.conf), which determines what connections are allowed. This allows control over which user can connect to which database, where they can connect from (IP address, IP address range, domain socket), which authentication system will be enforced, and whether the connection must use Transport Layer Security (TLS).

Standards compliance[edit]

PostgreSQL claims high, but not complete, conformance with the latest SQL standard ("as of the version 15 release in October 2022, PostgreSQL conforms to at least 170 of the 179 mandatory features for SQL:2016 Core conformance", and no other databases fully conformed to it[79]). One exception is the handling of unquoted identifiers like table or column names. In PostgreSQL they are folded, internally, to lower case characters[80] whereas the standard says that unquoted identifiers should be folded to upper case. Thus, Foo should be equivalent to FOO not foo according to the standard. Other shortcomings concern the absence of temporal tables allowing automatic logging of row versions during transactions with the possibility of browsing in time (FOR SYSTEM TIME predicate),[citation needed] although relatively SQL compliant third-party extensions are available.[16]

Benchmarks and performance[edit]

Many informal performance studies of PostgreSQL have been done.[81] Performance improvements aimed at improving scalability began heavily with version 8.1. Simple benchmarks between version 8.0 and version 8.4 showed that the latter was more than ten times faster on read-only workloads and at least 7.5 times faster on both read and write workloads.[82]

The first industry-standard and peer-validated benchmark was completed in June 2007, using the Sun Java System Application Server (proprietary version of GlassFish) 9.0 Platform Edition, UltraSPARC T1-based Sun Fire server and PostgreSQL 8.2.[83] This result of 778.14 SPECjAppServer2004 JOPS@Standard compares favourably with the 874 JOPS@Standard with Oracle 10 on an Itanium-based HP-UX system.[81]

In August 2007, Sun submitted an improved benchmark score of 813.73 SPECjAppServer2004 JOPS@Standard. With the system under test at a reduced price, the price/performance improved from $84.98/JOPS to $70.57/JOPS.[84]

The default configuration of PostgreSQL uses only a small amount of dedicated memory for performance-critical purposes such as caching database blocks and sorting. This limitation is primarily because older operating systems required kernel changes to allow allocating large blocks of shared memory.[85] PostgreSQL.org provides advice on basic recommended performance practice in a wiki.[86]

In April 2012, Robert Haas of EnterpriseDB demonstrated PostgreSQL 9.2's linear CPU scalability using a server with 64 cores.[87]

Matloob Khushi performed benchmarking between PostgreSQL 9.0 and MySQL 5.6.15 for their ability to process genomic data. In his performance analysis he found that PostgreSQL extracts overlapping genomic regions eight times faster than MySQL using two datasets of 80,000 each forming random human DNA regions. Insertion and data uploads in PostgreSQL were also better, although general searching ability of both databases was almost equivalent.[88]

Platforms[edit]

PostgreSQL is available for the following operating systems: Linux (all recent distributions), 64-bit ARM and x86-64 installers available and tested for macOS (OS X)[89] version 10.12 and newer, Windows (with installers available and tested for 64-bit Windows Server 2019 and 2016; some older PostgreSQL versions were tested back to Windows 2012 R2[90]), FreeBSD, OpenBSD,[91] NetBSD, and these without official (though unofficial likely available) binary executables, Solaris,[92] AIX, and HP-UX.[93] Most other (modern) Unix-like systems do also work.

PostgreSQL can be expected to work on any of the following instruction set architectures (and operating systems): 64-bit x86-64 and 32-bit x86 on Windows XP (or later) and other operating systems; these are supported on other than Windows: 64-bit ARM[94] and the older 32-bit ARM, including older such as ARMv6 in Raspberry Pi[95]), z/Architecture, S/390, PowerPC (incl. 64-bit Power ISA), SPARC (also 64-bit), IA-64 Itanium (HP-UX), MIPS and PA-RISC. It was also known to work on some other platforms (while not been tested on for years, i.e. for latest versions).[96]

Database administration[edit]

Open source front-ends and tools for administering PostgreSQL include:

psql
The primary front-end for PostgreSQL is the psql command-line program, which can be used to enter SQL queries directly, or execute them from a file. In addition, psql provides a number of meta-commands and various shell-like features to facilitate writing scripts and automating a wide variety of tasks; for example tab completion of object names and SQL syntax.
pgAdmin
The pgAdmin package is a free and open-source graphical user interface (GUI) administration tool for PostgreSQL, which is supported on many computer platforms.[97] The program is available in more than a dozen languages. The first prototype, named pgManager, was written for PostgreSQL 6.3.2 from 1998, and rewritten and released as pgAdmin under the GNU General Public License (GPL) in later months. The second incarnation (named pgAdmin II) was a complete rewrite, first released on January 16, 2002. The third version, pgAdmin III, was originally released under the Artistic License and then released under the same license as PostgreSQL. Unlike prior versions that were written in Visual Basic, pgAdmin III is written in C++, using the wxWidgets[98] framework allowing it to run on most common operating systems. The query tool includes a scripting language called pgScript for supporting admin and development tasks. In December 2014, Dave Page, the pgAdmin project founder and primary developer,[99] announced that with the shift towards web-based models, work has begun on pgAdmin 4 with the aim to facilitate cloud deployments.[100] In 2016, pgAdmin 4 was released. The pgAdmin 4 backend was written in Python, using Flask and the Qt framework.[101]
phpPgAdmin
phpPgAdmin is a web-based administration tool for PostgreSQL written in PHP and based on the popular phpMyAdmin interface originally written for MySQL administration.[102]
PostgreSQL Studio
PostgreSQL Studio allows users to perform essential PostgreSQL database development tasks from a web-based console. PostgreSQL Studio allows users to work with cloud databases without the need to open firewalls.[103]
TeamPostgreSQL
AJAX/JavaScript-driven web interface for PostgreSQL. Allows browsing, maintaining and creating data and database objects via a web browser. The interface offers tabbed SQL editor with autocompletion, row editing widgets, click-through foreign key navigation between rows and tables, favorites management for commonly used scripts, among other features. Supports SSH for both the web interface and the database connections. Installers are available for Windows, Macintosh, and Linux, and a simple cross-platform archive that runs from a script.[104]
LibreOffice, OpenOffice.org
LibreOffice and OpenOffice.org Base can be used as a front-end for PostgreSQL.[105][106]
pgBadger
The pgBadger PostgreSQL log analyzer generates detailed reports from a PostgreSQL log file.[107]
pgDevOps
pgDevOps is a suite of web tools to install & manage multiple PostgreSQL versions, extensions, and community components, develop SQL queries, monitor running databases and find performance problems.[108]
Adminer
Adminer is a simple web-based administration tool for PostgreSQL and others, written in PHP.
pgBackRest
pgBackRest is a backup and restore tool for PostgreSQL that provides support for full, differential, and incremental backups.[109]
pgaudit
pgaudit is a PostgreSQL extension that provides detailed session and/or object audit logging via the standard logging facility provided by PostgreSQL.[110]
WAL-E
WAL-E is a backup and restore tool for PostgreSQL that provides support for physical (WAL-based) backups, written in Python.[111]

A number of companies offer proprietary tools for PostgreSQL. They often consist of a universal core that is adapted for various specific database products. These tools mostly share the administration features with the open source tools but offer improvements in data modeling, importing, exporting or reporting.

Notable users[edit]

Notable organizations and products that use PostgreSQL as the primary database include:

Service implementations[edit]

Some notable vendors offer PostgreSQL as software as a service:

  • Heroku, a platform as a service provider, has supported PostgreSQL since the start in 2007.[137] They offer value-add features like full database roll-back (ability to restore a database from any specified time),[138] which is based on WAL-E, open-source software developed by Heroku.[139]
  • In January 2012, EnterpriseDB released a cloud version of both PostgreSQL and their own proprietary Postgres Plus Advanced Server with automated provisioning for failover, replication, load-balancing, and scaling. It runs on Amazon Web Services.[140] Since 2015, Postgres Advanced Server has been offered as ApsaraDB for PPAS, a relational database as a service on Alibaba Cloud.[141]
  • VMware has offered vFabric Postgres (also termed vPostgres[142]) for private clouds on VMware vSphere since May 2012.[143] The company announced End of Availability (EOA) of the product in 2014.[144]
  • In November 2013, Amazon Web Services announced the addition of PostgreSQL to their Relational Database Service offering.[145][146]
  • In November 2016, Amazon Web Services announced the addition of PostgreSQL compatibility to their cloud-native Amazon Aurora managed database offering.[147]
  • In May 2017, Microsoft Azure announced Azure Databases for PostgreSQL.[148]
  • In May 2019, Alibaba Cloud announced PolarDB for PostgreSQL.[149]
  • Jelastic Multicloud Platform as a Service has provided container-based PostgreSQL support since 2011. It also offers automated asynchronous master-slave replication of PostgreSQL.[150]
  • In June 2019, IBM Cloud announced IBM Cloud Hyper Protect DBaaS for PostgreSQL.[151]
  • In September 2020, Crunchy Data announced Crunchy Bridge.[152]
  • In June 2022, Neon.tech announced Neon Serverless Postgres.[153]

Release history[edit]

Release history
Release First release Latest minor version Latest release End of
life[154]
Milestones
6.0 1997-01-29 First formal release of PostgreSQL, unique indexes, pg_dumpall utility, ident authentication
6.1 1997-06-08 Old version, no longer maintained: 6.1.1 1997-07-22 Multicolumn indexes, sequences, money data type, GEQO (GEnetic Query Optimizer)
6.2 1997-10-02 Old version, no longer maintained: 6.2.1 1997-10-17 JDBC interface, triggers, server programming interface, constraints
6.3 1998-03-01 Old version, no longer maintained: 6.3.2 1998-04-07 2003-03-01 SQL-92 subselect ability, PL/pgTCL
6.4 1998-10-30 Old version, no longer maintained: 6.4.2 1998-12-20 2003-10-30 VIEWs (then only read-only) and RULEs, PL/pgSQL
6.5 1999-06-09 Old version, no longer maintained: 6.5.3 1999-10-13 2004-06-09 MVCC, temporary tables, more SQL statement support (CASE, INTERSECT, and EXCEPT)
7.0 2000-05-08 Old version, no longer maintained: 7.0.3 2000-11-11 2004-05-08 Foreign keys, SQL-92 syntax for joins
7.1 2001-04-13 Old version, no longer maintained: 7.1.3 2001-08-15 2006-04-13 Write-ahead log, outer joins
7.2 2002-02-04 Old version, no longer maintained: 7.2.8 2005-05-09 2007-02-04 PL/Python, OIDs no longer required, internationalization of messages
7.3 2002-11-27 Old version, no longer maintained: 7.3.21 2008-01-07 2007-11-27 Schema, table function, prepared query[155]
7.4 2003-11-17 Old version, no longer maintained: 7.4.30 2010-10-04 2010-10-01 Optimization on JOINs and data warehouse functions[156]
8.0 2005-01-19 Old version, no longer maintained: 8.0.26 2010-10-04 2010-10-01 Native server on Microsoft Windows, savepoints, tablespaces, point-in-time recovery[157]
8.1 2005-11-08 Old version, no longer maintained: 8.1.23 2010-12-16 2010-11-08 Performance optimization, two-phase commit, table partitioning, index bitmap scan, shared row locking, roles
8.2 2006-12-05 Old version, no longer maintained: 8.2.23 2011-12-05 2011-12-05 Performance optimization, online index builds, advisory locks, warm standby[158]
8.3 2008-02-04 Old version, no longer maintained: 8.3.23 2013-02-07 2013-02-07 Heap-only tuples, full text search,[159] SQL/XML, ENUM types, UUID types
8.4 2009-07-01 Old version, no longer maintained: 8.4.22 2014-07-24 2014-07-24 Window functions, column-level permissions, parallel database restore, per-database collation, common table expressions and recursive queries[160]
9.0 2010-09-20 Old version, no longer maintained: 9.0.23 2015-10-08 2015-10-08 Built-in binary streaming replication, hot standby, in-place upgrade ability, 64-bit Windows[161]
9.1 2011-09-12 Old version, no longer maintained: 9.1.24 2016-10-27 2016-10-27 Synchronous replication, per-column collations, unlogged tables, serializable snapshot isolation, writeable common table expressions, SELinux integration, extensions, foreign tables[162]
9.2 2012-09-10[163] Old version, no longer maintained: 9.2.24 2017-11-09 2017-11-09 Cascading streaming replication, index-only scans, native JSON support, improved lock management, range types, pg_receivexlog tool, space-partitioned GiST indexes
9.3 2013-09-09 Old version, no longer maintained: 9.3.25 2018-11-08 2018-11-08 Custom background workers, data checksums, dedicated JSON operators, LATERAL JOIN, faster pg_dump, new pg_isready server monitoring tool, trigger features, view features, writeable foreign tables, materialized views, replication improvements
9.4 2014-12-18 Old version, no longer maintained: 9.4.26 2020-02-13 2020-02-13 JSONB data type, ALTER SYSTEM statement for changing config values, ability to refresh materialized views without blocking reads, dynamic registration/start/stop of background worker processes, Logical Decoding API, GiN index improvements, Linux huge page support, database cache reloading via pg_prewarm, reintroducing Hstore as the column type of choice for document-style data.[164]
9.5 2016-01-07 Old version, no longer maintained: 9.5.25 2021-02-11 2021-02-11 UPSERT, row level security, TABLESAMPLE, CUBE/ROLLUP, GROUPING SETS, and new BRIN index[165]
9.6 2016-09-29 Old version, no longer maintained: 9.6.24 2021-11-11 2021-11-11 Parallel query support, PostgreSQL foreign data wrapper (FDW) improvements with sort/join pushdown, multiple synchronous standbys, faster vacuuming of large table
10 2017-10-05 Old version, no longer maintained: 10.23 2022-11-10 2022-11-10 Logical replication,[166] declarative table partitioning, improved query parallelism
11 2018-10-18 Old version, no longer maintained: 11.22 2023-11-09 2023-11-09 Increased robustness and performance for partitioning, transactions supported in stored procedures, enhanced abilities for query parallelism, just-in-time (JIT) compiling for expressions[167][168]
12 2019-10-03 Older version, yet still maintained: 12.19 2024-05-09 2024-11-14 Improvements to query performance and space utilization; SQL/JSON path expression support; generated columns; improvements to internationalization, and authentication; new pluggable table storage interface.[169]
13 2020-09-24 Older version, yet still maintained: 13.15 2024-05-09 2025-11-13 Space savings and performance gains from de-duplication of B-tree index entries, improved performance for queries that use aggregates or partitioned tables, better query planning when using extended statistics, parallelized vacuuming of indexes, incremental sorting[170][171]
14 2021-09-30 Older version, yet still maintained: 14.12 2024-05-09 2026-11-12 Added SQL-standard SEARCH and CYCLE clauses for common table expressions, allow DISTINCT to be added to GROUP BY[172][173]
15 2022-10-13 Older version, yet still maintained: 15.7 2024-05-09 2027-11-11 Implements SQL-standard MERGE statement. PL/Python now only supports current Python 3, and plpythonu now means Python 3, no longer the discontinued Python 2.
16 2023-09-14 Current stable version: 16.3 2024-05-09 2028-11-09 Improvements to logical replication, pg_stat_io view (for I/O metrics)[174]
17 Future release: 17.0 2024-05-23
Legend:
Old version
Older version, still maintained
Latest version
Latest preview version
Future release

See also[edit]

References[edit]

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Further reading[edit]

External links[edit]