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Re: Linux/PostgreSQL scalability issue - problem with 8 cores

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jakub Ouhrabka <kuba(at)comgate(dot)cz>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Linux/PostgreSQL scalability issue - problem with 8 cores
Date: 2008-01-03 16:59:30
Message-ID: 7083.1199379570@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Jakub Ouhrabka <kuba(at)comgate(dot)cz> writes:
> we have a PostgreSQL dedicated Linux server with 8 cores (2xX5355). We 
> came accross a strange issue: when running with all 8 cores enabled 
> approximatly once a minute (period differs) the system is very busy for 
> a few seconds (~5-10s) and we don't know why - this issue don't show up 
> when we tell Linux to use only 2 cores, with 4 cores the problem is here 
> but it is still better than with 8 cores - all on the same machine, same 
> config, same workload. We don't see any apparent reason for these peaks. 

Interesting.  Maybe you could use oprofile to try to see what's
happening?  It sounds a bit like momentary contention for a spinlock,
but exactly what isn't clear.

> Can this be connected with our heavy use of listen/notify and hundreds 
> backends in listen mode?

Perhaps.  Have you tried logging executions of NOTIFY to see if they are
correlated with the spikes?

			regards, tom lane

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Next:From: Jakub OuhrabkaDate: 2008-01-03 17:37:29
Subject: Re: Linux/PostgreSQL scalability issue - problem with 8 cores
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Subject: Re: Commit takes a long time.

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