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Re: Proposal of PITR performance improvement for 8.4.

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Koichi Suzuki <koichi(dot)szk(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Proposal of PITR performance improvement for 8.4.
Date: 2008-10-28 23:54:21
Message-ID: 87zlko8edu.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:

> On Tue, 2008-10-28 at 17:40 -0400, Bruce Momjian wrote:
>> Gregory Stark wrote:
>> > Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>> > 
>> > > I'm happy with the idea of a readahead process. I thought we were
>> > > implementing a BackgroundReader process for other uses. Is that dead
>> > > now?
>> > 
>> > You and Bruce seem to keep resurrecting that idea. I've never liked it -- I
>> > always hated that in Oracle and thought it was a terrible kludge.
>> 
>> I didn't think I was promoting the separate reader process after you had
>> the posix_fadvise() idea.

I'm sorry, I thought I remembered you mentioning it again. But perhaps I was
thinking of someone else (perhaps it was Simon again?) or perhaps it was
before you saw the actual patch.

> It would be good if the solutions for normal running and recovery were
> similar. Greg, please could you look into that?

I could do the readahead side of things but what I'm not sure how to arrange
is how to restructure the wal reading logic to read records ahead of the
actual replay.

I think we would have to maintain two pointers one for the prefetch and one
for the actual running. But the logic in for recovery is complex enough that
I'm concerned about changing it enough to do that and whether it can be done
without uglifying the code quite a bit.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's RemoteDBA services!

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