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Re: checkpoint segments

From: Alvaro Herrera <alvherre(at)surnet(dot)cl>
To: David Parker <dparker(at)tazznetworks(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: checkpoint segments
Date: 2005-05-16 04:39:20
Message-ID: 20050516043920.GA9292@surnet.cl (view raw, whole thread or download thread mbox)
Thread:
Lists: pgsql-performance
On Sun, May 15, 2005 at 08:22:13PM -0400, David Parker wrote:

> In the database log at that time there was a "recycling transaction log"
> message which seems to correspond to the time when the clients were
> paused, though I don't have it concretely correlated. 

Maybe what you need is make the bgwriter more aggressive, so that I/O is
more evenly spread between checkpoint intervals -- that way, at
checkpoint there's less work to do.

> I've seen these messages in the log before, and am aware of the need to
> increase checkpoint_segments, but I wasn't aware that recycling a
> transaction log could be that damaging to performance. There may have
> been some local hiccup in this case, but I'm wondering if recycling is
> known to be a big hit in general, and if I should strive to tune so that
> it never happens (if that's possible)?

Well, recycling is actually a *good* thing -- it saves you from having
to remove WAL segment files and allocate new files for the new logs.  So
what you really want doesn't have anything to do with the recycling
itself, but rather with the simultaneous checkpoint that's going on at
the same time.

-- 
Alvaro Herrera (<alvherre[a]surnet.cl>)
Licensee shall have no right to use the Licensed Software
for productive or commercial use. (Licencia de StarOffice 6.0 beta)

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