From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, Andrew Dunstan <andrew(at)dunslane(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: lock contention on parallel COPY ? |
Date: | 2008-09-26 17:56:36 |
Message-ID: | 1222451796.4445.990.camel@ebony.2ndQuadrant |
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Lists: | pgsql-hackers |
On Fri, 2008-09-26 at 12:38 -0400, Tom Lane wrote:
> Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc> writes:
> > heh no log archiving - I actually said that I'm now playing with
> > --truncate-before-load which seems to cause a noticeable performance (as
> > in IO generated) increase but I still see >130000 context switches/s and
> > a profile that looks like:
>
> > samples % symbol name
> > 55526 16.5614 LWLockAcquire
> > 29721 8.8647 DoCopy
> > 26581 7.9281 CopyReadLine
> > 25105 7.4879 LWLockRelease
> > 15743 4.6956 PinBuffer
> > 14725 4.3919 heap_formtuple
>
> Still a lot of contention for something, then. You might try turning on
> LWLOCK_STATS (this only requires recompiling storage/lmgr/lwlock.c) to
> get some evidence about what.
Probably loading a table with a generated PK or loading data in
ascending sequence, so its contending heavily for the rightmost edge of
the index.
We need to load data a block at a time and buffer the inserts into the
index also, so we don't need to lock/unlock per row.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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