IDMS: SQL index changes during REORG or unload/reload

Products

• IDMS

Issue/Introduction

This document describes how to make any physical definition changes to indexes when running REORG or unload/reload to expand an SQL-defined database.

Environment

IDMS, any supported release.

Resolution

In a non-SQL defined IDMS database, there is a logical/physical separation which allows physical index characteristics to be specified in the physical entities (segment and DMCL) which in most cases are by definition already changing as a result of the maintenance being performed.

This is not the case in an SQL-defined database. The physical characteristics (INDEX BLOCK CONTAINS and DISPLACEMENT) are specified in the index itself. So the question arises, how, or more specifically when, does one make any required changes to index characteristics when performing such maintenance.

The answer is that any ALTER INDEX statements making such changes should be done prior to the maintenance. At that point, in theory, the database may not match the new physical attributes, but for retrieval access (the "unload") this does not matter. The existing index can be read successfully regardless of how these values are set. They are only relevant to the reload (i.e. when SR8s should split and where new SR8s should be located).