MaxDB Parameter RestartVolumeGroupingMemorySize

[andreas_zigann]

Hello,

as of patch MaxDB 7.9.08.11 this parameter speeds up the restart of the database. I could even verify this, with a database usually needed 15 minutes to start and now starts within 5 minutes.

Unfortunately I can not find a useful documentation of this parameter. So I have a few questions.

Which value should be used (even default value 0 seems to speed up the start of the database)?

Which influence has this parameter to the database (smaller cache usage, higher impact at starting, any dangers)?

Has anyone got experience with this parameter?

Best Regards

Andreas

[yashwanthkumar_kethineed · Accepted solution]

Hello Andreas,

The value of this parameter (RestartVolumeGroupingMemorySize) defines the amount of memory (in KB) used for grouping of used blocks by volume in the course of a system restart. Using this kind of grouping may speed up the restart in case of huge databases. The default value of 0 means that no grouping by volume takes place.

This parameter potentially improves restart performance, but only in those (rare) cases when the system is CPU bound during restart (we would normally expect it to be IO bound). Increasing this parameter will allocate more memory in one chunk, which we have seen to be benefitial on Solaris OS. If you have any system with long restart times, create a SAP message and we will check, if there is room for improvement, otherwise, just leave the parameter value at its default of '0'.

For more information run "param_getfull RestartVolumeGroupingMemorySize"

Regards, Yashwanth

[andreas_zigann · Accepted solution]

Thank you Yashwanth,

I will open 2 customer messages, each for one problematic productive system.

I wonder one thing:

At QAS system I set the Parameter to 10 GB (at 64 GB Cache Size). As expected the system startup speeds up to 5 minutes. Before the database patch from 7.9.8.7 to 7.9.8.11 the start needs between 15 and 20 minutes.

At PRD system I did not set the parameter, because I had not found properly information which value may be recommended. I was afraid to waste cache size. The system startup speeds up to 5 minutes, too.

What I am missing in documentaion of this parameter:

Where is the cache located? e.g. Cache-Size, Catalog-Cache, seperated

Which value is recommended? e.g. 10% Cache Size, 100 MB, 50% Catalog size, 1 % database size

Are there any risks? e.g. wasting memory, database consitency, performance issues

If this parameter should not be used except of recommendation by SAP support, I would like to have this told in documentation.

Best Regards

Andreas