COMMIT of updates when using MEMORY CACHE

Products

• IDMS
• IDMS - Database

Issue/Introduction

When defining a file to use the MEMORY CACHE feature in the DMCL, do committed updates get written to the DASD at the same time as they are written to the MEMORY CACHE, or could there be a delay writing to the DASD?

When considering implementing the MEMORY CACHE feature for a database area which is a heavily hit area, the concern is with the implications of an IDMS or MVS system crash with regards to database integrity.

Namely, when a page is written back to the IDMS buffer and a commit is issued, the page is then written back to the cache.

At this point will the page also be written back to the database file in a synchronous fashion?

 

Environment

Release: All supported releases.

Resolution

All updates go to the database buffers regardless of the use of caching. Before any database buffer is written, the physical journal write must be completed. When the buffer is finally written it is written to cache and to the physical file at the same time. There is no danger of the cache containing committed updates that are not on the physical file. Completion of the journal I/O prior to the database pages being written ensures proper recoverability.

 

 

Additional Information

Buffer Management