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Re: Decreasing WAL size effects

From: Kyle Cordes <kyle(at)kylecordes(dot)com>
To: pgsql <pgsql-general(at)postgresql(dot)org>
Subject: Re: Decreasing WAL size effects
Date: 2008-10-30 20:42:59
Message-ID: 490A1C53.7040602@kylecordes.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
Greg Smith wrote:

> there's no chance it can accidentally look like a valid segment.  But 
> when an existing segment is recycled, it gets a new header and that's 
> it--the rest of the 16MB is still left behind from whatever was in that 
> segment before.  That means that even if you only write, say, 1MB of new 

[...]

> What clearxlogtail does is look inside the WAL segment, and it clears 
> the "tail" behind the portion of that is really used.  So our example 
> file would end up with just the 1MB of useful data, followed by 15MB of 


It sure would be nice if there was a way for PG itself to zero the 
unused portion of logs as they are completed, perhaps this will make it 
in as part of the ideas discussed on this list a while back to make a 
more "out of the box" log-ship mechanism?


-- 
Kyle Cordes
http://kylecordes.com

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