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To: Jakub Ouhrabka <kuba@comgate.cz>
cc: pgsql-performance@postgresql.org
Subject: Re: Linux/PostgreSQL scalability issue - problem with 8 cores 
In-reply-to: <4782063C.7070105@comgate.cz> 
References: <flii57$748$1@news.hub.org> <7083.1199379570@sss.pgh.pa.us>
	<477D1D59.7050002@comgate.cz> <4782063C.7070105@comgate.cz>
Comments: In-reply-to Jakub Ouhrabka <kuba@comgate.cz>
	message dated "Mon, 07 Jan 2008 12:00:12 +0100"
Date: Mon, 07 Jan 2008 17:31:30 -0500
Message-ID: <26502.1199745090@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Jakub Ouhrabka <kuba@comgate.cz> writes:
> We've tried several times to get stacktrace from some of the running 
> backends during spikes, we got always this:

> 0x00002b005d00a9a9 in semop () from /lib/libc.so.6
> #0  0x00002b005d00a9a9 in semop () from /lib/libc.so.6
> #1  0x000000000054fe53 in PGSemaphoreLock (sema=0x2b00a04e5090, 
> interruptOK=0 '\0') at pg_sema.c:411
> #2  0x0000000000575d95 in LWLockAcquire (lockid=SInvalLock, 
> mode=LW_EXCLUSIVE) at lwlock.c:455
> #3  0x000000000056fbfe in ReceiveSharedInvalidMessages 
> (invalFunction=0x5e9a30 <LocalExecuteInvalidationMessage>,
>     resetFunction=0x5e9df0 <InvalidateSystemCaches>) at sinval.c:159
> #4  0x0000000000463505 in StartTransactionCommand () at xact.c:1439
> #5  0x000000000056fa4b in ProcessCatchupEvent () at sinval.c:347
> #6  0x000000000056fb20 in CatchupInterruptHandler 
> (postgres_signal_arg=<value optimized out>) at sinval.c:221

CatchupInterruptHandler, eh?  That seems to let NOTIFY off the hook, and
instead points in the direction of sinval processing; which is to say,
propagation of changes to system catalogs.  Does your app create and
destroy a tremendous number of temp tables, or anything else in the way
of frequent DDL commands?

			regards, tom lane