MyISAM
MyISAM (My Indexed Sequential Access Method) is a storage engine in the MySQL database management system . It is based on the older ISAM system with a few extensions and was the standard storage engine up to MySQL 5.1. From version 5.5 onwards it was replaced by InnoDB as the standard storage engine.
properties
MyISAM is characterized by its high efficiency compared to other table types supported by MySQL and, from version 3.23.23 of MySQL, supports a powerful full-text search. MyISAM is also recommended for tables that are read significantly more frequently (SELECT) than written to them (INSERT / UPDATE). MyISAM supports in contrast to z. B. InnoDB no transactions , so that in the event of an error, inconsistent data can remain in the database, if some of several related queries have already been executed and others have not. MyISAM also does not offer referential integrity .
For each MyISAM table, three files are created in the file system. The names of each of the files consist of the name of the table and a file name extension that identifies the file type: For the table definition .frm, for the data .MYD(MYData) and for the index .MYI(MyIndex).
In order to explicitly create a MyISAM table, the option can be specified in SQLENGINE :
CREATE TABLE t (i INT) ENGINE = MYISAM;
(Note: Older versions of MySQL use the keyword TYPEinstead of ENGINE(Example:) TYPE = MYISAM. MySQL 5.0 and 5.1 support this syntax backwards compatible, but the use of is ENGINErecommended. As of MySQL 5.5, only the keyword is ENGINEsupported.)
The use of ENGINEis optional. If not specified, the table type stored in the default settings is used. MySQL 5.5 and higher uses InnoDB by default .
Individual evidence
- ↑ http://www.oracle.com/us/corporate/press/195726
- ↑ see e.g. B. Pachev: Understanding MySQL Internals, Chapter 10: Storage Engines
- ↑ Archived copy ( memento of the original from January 29, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ http://dev.mysql.com/doc/refman/5.5/en/create-table.html
literature
- Sasha Pachev: Understanding MySQL Internals, O'Reilly 2007, ISBN 978-0-596-00957-1