Re: Benchmarking: How to identify bottleneck (limiting factor) andachieve "linear scalability"? - Mailing list pgsql-performance

From Saurabh Nanda
Subject Re: Benchmarking: How to identify bottleneck (limiting factor) andachieve "linear scalability"?
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Msg-id CAPz=2oF+pVeaxG6RmouZ0idQ31ZSLq+8sXNTS2ggoGoHZtwxpg@mail.gmail.com
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In response to Re: Benchmarking: How to identify bottleneck (limiting factor) andachieve "linear scalability"?  (Justin Pryzby <pryzby@telsasoft.com>)
List pgsql-performance
 
Do you know which of the settings is causing lower TPS ? 

I suggest to check shared_buffers.

I'm trying to find this, but it's taking a lot of time in re-running the benchmarks changing one config setting at a time. Thanks for the tip related to shared_buffers.
 

If you haven't done it, disabling THP and KSM can resolve performance issues,
esp. with large RAM like shared_buffers, at least with older kernels.
https://www.postgresql.org/message-id/20170718180152.GE17566%40telsasoft.com

Is this a well-known performance "hack"? Is there any reason why it is not mentioned at https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server ? Are the stability implications of fiddling with THP and KSM well-known? Also, wrt KSM, my understand was that when a process forks the process' memory is anyways "copy on write", right? What other kind of pages would end-up being de-duplicated by ksmd? (Caveat: This is the first time I'm hearing about KSM and my knowledge is based off a single reading of https://www.kernel.org/doc/html/latest/admin-guide/mm/ksm.html )

-- Saurabh.

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