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Re: Decreasing WAL size effects

From: Jason Long <mailing(dot)list(at)supernovasoftware(dot)com>
To: Kyle Cordes <kyle(at)kylecordes(dot)com>
Cc: pgsql <pgsql-general(at)postgresql(dot)org>
Subject: Re: Decreasing WAL size effects
Date: 2008-10-30 20:51:18
Message-ID: 490A1E46.1080107@supernovasoftware.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
Kyle Cordes wrote:
> 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?
*I agree totally.  I looked at the code for clearxlogtail and it seems 
short and not very complex.  Hopefully something like this will at least 
be a trivial to set up option in 8.4.**
*
>
>

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