From: Pierre C <lists@peufeu.com>
To: Josh Berkus <josh@agliodbs.com>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Wrong docs on wal_buffers?
Date: Wed, 05 Jan 2011 23:58:32 +0100
Message-ID: <op.voux3uooeorkce@apollo13> (raw)
In-Reply-To: <AANLkTi=YLCEGcwa-9hFYykRgTfUVDhZrwNGo7qaJZnRC@mail.gmail.com>
References: <4D24D7DE.6020507@agliodbs.com>
<AANLkTi=YLCEGcwa-9hFYykRgTfUVDhZrwNGo7qaJZnRC@mail.gmail.com>
> And the risks are rather asymmetric. I don't know of any problem from
> too large a buffer until it starts crowding out shared_buffers, while
> under-sizing leads to the rather drastic performance consequences of
> AdvanceXLInsertBuffer having to wait on the WALWriteLock while holding
> the WALInsertLock,
Suppose you have a large update which generates lots of WAL, some WAL
segment switching will take place, and therefore some fsync()s. If
wal_buffers is small enough that it fills up during the time it takes to
fsync() the previous WAL segment, isn't there a risk that all WAL writes
are stopped, waiting for the end of this fsync() ?
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To: pgsql-performance@postgresql.org
Cc: lists@peufeu.com, josh@agliodbs.com, jeff.janes@gmail.com
Subject: Re: Wrong docs on wal_buffers?
In-Reply-To: <op.voux3uooeorkce@apollo13>
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