The most efficient option for MAINTAIN INDEX

Products

• IDMS
• IDMS - Database

Issue/Introduction

When re-building a system-owned index for performance purposes, is it more efficient to rebuild the index FROM INDEX or FROM MEMBERS?

Environment

Release: All supported releases.

Resolution

As long as the integrity of an index is intact, it is almost always more efficient to run the MAINTAIN INDEX utility as a REBUILD FROM INDEX rather than REBUILD FROM MEMBERS. When performing a REBUILD FROM INDEX the utility will use the existing index structure to extract symbolic key information while FROM MEMBERS requires that the database area of the member record is swept resulting in more physical I/O operations during the extract phase of the process. There is no difference in the amount of work generated during the steps that recreate the index structure. If there is any question about the integrity of the existing index structure a REBUILD FROM MEMBERS should be used.

Note: REBUILD FROM ALLROWS is the same as MEMBERS, except that for an index which is not MANDATORY AUTOMATIC, all records of the member type will be connected to the index, regardless of whether they were in the index prior to the MAINTAIN INDEX or not.