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Re: futex

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Manfred Spraul <manfred(at)colorfullife(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: futex
Date: 2004-08-25 17:27:11
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Lists: pgsql-hackers

> What did you test exactly and could you explain a bit about the context
> switch storm?

PostgreSQL currently causes a CS storm (context switches > 100,000) on 
multi-processor machines where you have a number of concurrent processes ( > 
than the number of processors) accessing the same small quantity of data 
repeatedly, particularly if doing seq scans and/or bad queries.   This issue 
causes a significant drop in server performance, as much as 60%.  

> Did you use the futex interface directly or pthread_rwlock_rdlock?

I'll have to admit to having only a beginner's grasp of this stuff, but I do 
believe that that was what the OSDL patch did.   Jan also tried a simpler 
patch, which didn't work either.    Both Jan and Tom have expressed the 
opinion that the only solution is to make the BufrMgrLock more granular (as 
in, not monolithic) but this is a huge task.

Josh Berkus
Aglio Database Solutions
San Francisco

In response to

  • Re: futex at 2004-08-25 17:14:53 from Manfred Spraul


  • Re: futex at 2004-08-25 22:26:28 from Neil Conway

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