HALDB

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HALDB (High Availability Large Database) is a database type at IMS that IBM introduced with IMS Version 7.

Size limit

A special feature of a HALDB is the possibility of partitioning. A HALDB can be divided into more than a thousand partitions (when introduced: 1001). Each partition can consist of up to 10 data groups with a maximum of 4 gigabytes of data each. This results in a maximum size of 1001 * 10 * 4 gigabytes.

Partitioning

Each database record has a unique key . Using this and predefined key limits, the database system automatically determines the associated partition for each database record. Alternatively, a self-written routine for the distribution (Partition Selection Exit - PSE) can be made known to the database system for each database.

HALDB types

PHIDAM (Partitioned HIDAM)

Each partition has a primary index ( HIDAM stands for Hierarchical Index Direct Access Method ). This means that there is direct access via an index. possible.

PHDAM (Partitioned HDAM)

Although there is no index, direct access is possible using a hash function (randomizing routine). For each data record it calculates the position within the database partition where it should be. At Allianz, W. Fritsch developed a process called WMP ( Woifis Magic Partitioning ), with which the storage sequence across all partitions is independent of the number of partitions and is identical to that of an (unpartitioned) HDAM DB with randomizing routine DFSHDC40.

PSINDEX (Partitioned Secondary Index)

Optionally, 0 to n secondary indexes (PSINDEX) can be defined for each PDHAM or PHIDAM database .

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