ISAM pools in data spaces

The creation of buffer areas for NK-ISAM files (ISAM pools) which are opened with SHARUPD=YES is automated and optimized. The explicit configuration of ISAM pools via the relevant program or command interfaces can thus be dispensed with.

ISAM pools are created on a file-specific basis the first time a file is opened. When a file is opened, a suitable section of a data space is initialized as an ISAM pool. In the course of this the size is determined automatically:
A data space with a total size of max. 2 GB is split into equal-sized sections of 1 MB (or a 2ⁿ multiple of this).

An ISAM pool consists of at least one such section. Depending on the file size an ISAM pool can also consist of several adjacent sections of this data space. The pool size is estimated using the formula on "Calculating the size of an ISAM pool".

It is also possible to define a size explicitly using the ADD-FILE-LINK ...,POOL-SIZE= command or via the relevant FILE program interface. However, this specification is only evaluated for ISAM pools in data spaces, in other words for file processing with SHARUPD=YES.

Commands and macros for cross-task user ISAM pools are still accepted for reasons of compatibility, but no longer result in such a pool being generated. Instead, DMS uses a standard ISAM pool in which the size specified beforehand by the user is not fallen below and the assignment of files to pools is retained.

The system administrator can use the SHOW-ISAM-CACHING command to obtain information on ISAM files buffered in privileged data spaces.