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Re: Load Distributed Checkpoints, take 3

From: Magnus Hagander <magnus(at)hagander(dot)net>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Greg Smith <gsmith(at)gregsmith(dot)com>,Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Load Distributed Checkpoints, take 3
Date: 2007-06-25 10:56:20
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Lists: pgsql-patches
On Mon, Jun 25, 2007 at 10:15:07AM +0100, Simon Riggs wrote:
> On Mon, 2007-06-25 at 01:33 -0400, Greg Smith wrote:
> > On Sun, 24 Jun 2007, Simon Riggs wrote:
> > 
> > > Greg can't choose to use checkpoint_segments as the limit and then 
> > > complain about unbounded recovery time, because that was clearly a 
> > > conscious choice.
> > 
> > I'm complaining 
> I apologise for using that emotive phrase.
> > only because everyone seems content to wander in a 
> > direction where the multiplier on checkpoint_segments for how many 
> > segments are actually active at once will go up considerably, which can 
> > make a known problem (recovery time) worse. 
> +50% more. Recovery time is a consideration that can be adjusted for. We
> have done nothing to make recovery rate worse; the additional WAL leads
> to an increased recovery time *only* if you keep the same parameter
> settings. There is no reason to keep them the same, nor do we promise
> that parameters will keep the exact meaning they had previous releases.
> As you say, we can put comments in the release notes to advise people of
> 50% increase in recovery time if the parameters stay the same. That
> would be balanced by the comment that checkpoints are now considerably
> smoother than before and more frequent checkpoints are unlikely to be a
> problem, so it is OK to reduce the parameters from the settings you used
> in previous releases.

Didn't we already add other featuers that makes recovery much *faster* than
before? In that case, are they faster enugh to neutralise this increased
time (a guestimate, of course)

Or did I mess that up with stuff we added for 8.2? :-)


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