Performance issue varying datashared areas to update

Products

• IDMS
• IDMS - Database

Issue/Introduction

Varying a very large datashared area can impact performance.

Environment

Release: All supported releases.

Cause

If a very large area with a large cache is varied from retrieval to update, all of the pages in the area must be purged from the cache because they can no longer be trusted to contain up-to-date data. 

In extreme cases, this can take a relatively long time (e.g. minutes) and negatively impact performance.

Resolution

Most likely the reason for the varying of the areas is to take backups.

In this case, it is recommended that instead of varying areas to retrieval, use one of the following methods to take backups:

• Hot backup, or
• QUIESCE the areas and task a cold backup. Using this method, the cold backup will be valid but will have the area lock on.

So when such a backup is restore, it will also need to be UNLOCKed.

These functions are documented at Backup Procedures.