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Enahncement to DB2_DEFER_MEMORY_COMMIT setting

See this idea on ideas.ibm.com

Regarding the use of DB2_DEFER_MEMORY_COMMIT=ON. This env variable will defer memory commitment, asynchronously in the background, for faster completion of ACTIVATE DATABASE. This helps to improve the database activation for large memory systems where in DB can take long time before opening DB for an application.

The Defer behavior applies to only buffer pools and locklist components where it has an overhead to database activation.

In 11.1 the default is OFF but changed 11.5.4.0 and 12.1 to ON by default. There is a lot more internal testing performed in 11.5 to support the change in behavior.

After db activation is complete and buffer pool memory has been committed the BPS (Buffer Pool Services) code doesn’t look at the setting again. Unless there is a ALTER BUFFERPOOL command to increase a buffer pool size and an additional shared memory segment is required to support the growth.

We encountered a critical issue where deferred memory allocation for the locklist caused the db2 instance to crash. Per IBM it was due to memory increase to locklist memory in deferred mode and post DB activation.

Although IBM has provided an alternative to restrict this setting to buffer pools only, we are concerned that similar issue may arise when buffer pool memory is increased after database activation, as such allocation are still deferred.

To mitigate this risk, we propose an enhancement to the DB2_DEFER_MEMORY_COMMIT functionality:-

1. Post database activation, all bufferpool memory allocations should handled synchronously.

2. Deferred memory allocation should not be allocated after the database is activate to prevent potential crashes.

This enhancement would provide a more robust solution, ensuring system stability while retaining the performance benefits this setting provides in initial database activation etc.

Thank you for your consideration and please let us know if you need any additional details on this request.

Thanks,

Pardeep Mehta

Needed By Month
  • Admin
    Siji Daniel
    Reply
    |
    Jan 6, 2025

    Thank you for submitting your request. We are reviewing this. Please expect an update in the portal within 90 days.
    Thank you.