Buffer assignments for native VSAM files
Article ID: 118854
Updated On:
Products
IDMS
IDMS - Database
Issue/Introduction
This article discusses best practices for assigning buffers to native VSAM files defined to a CA-IDMS CV.
When defining native VSAM files to IDMS, there are definitions made in the schema and DMCL similar to a normal IDMS database, including buffers.
However these definitions exist only to tell IDMS the nature of the VSAM file.
The buffering is not done in IDMS.
The buffer definitions in IDMS for native VSAM files are there only so that IDMS can construct the appropriate calls to VSAM.
The call is passed to VSAM and the buffering is maintained there.
When defining native VSAM files to IDMS, there are definitions made in the schema and DMCL similar to a normal IDMS database, including buffers.
However these definitions exist only to tell IDMS the nature of the VSAM file.
The buffering is not done in IDMS.
The buffer definitions in IDMS for native VSAM files are there only so that IDMS can construct the appropriate calls to VSAM.
The call is passed to VSAM and the buffering is maintained there.
Environment
CA IDMS, all supported releases.
Resolution
There are two types of VSAM buffers - LSR (local shared resources) and NSR (nonshared resources).
There can only be one LSR buffer defined in an IDMS CV.
Low activity native VSAM files should be assigned to that LSR buffer.
High activity native VSAM files should each be assigned to their own dedicated NSR buffer, except that when multiple IDMS files are mapped to the same native VSAM area definition, they must be assigned to the same buffer, otherwise the DMCL compile will fail with DB004063.
There can only be one LSR buffer defined in an IDMS CV.
Low activity native VSAM files should be assigned to that LSR buffer.
High activity native VSAM files should each be assigned to their own dedicated NSR buffer, except that when multiple IDMS files are mapped to the same native VSAM area definition, they must be assigned to the same buffer, otherwise the DMCL compile will fail with DB004063.
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