Re: COMMIT NOWAIT Performance Option

From: "Zeugswetter Andreas ADI SD" <ZeugswetterA(at)spardat(dot)at>
To: "Gregory Stark" <stark(at)enterprisedb(dot)com>
Cc: "Jeff Davis" <pgsql(at)j-davis(dot)com>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "Josh Berkus" <josh(at)agliodbs(dot)com>, <pgsql-hackers(at)postgresql(dot)org>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
Subject: Re: COMMIT NOWAIT Performance Option
Date: 2007-03-01 13:24:47
Message-ID: E1539E0ED7043848906A8FF995BDA57901CAFFBF@m0143.s-mxs.net
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> > Maybe a suitable replacement for full-page would be to sync the
first
> > WAL record for a page change before writing the buffer
>
> We *always* sync WAL records for page changes before writing
> the buffer for the page.

Um, is that so ? And how is that done ? (e.g. bgwriter would need to
wait for or even initiate a WAL record sync)
Seems this is not clear to others eighter.

Why else would people think we need a full data scan after crash without
full-pages ?
If this is true, all pages with possibly pending IO during crash will be
touched and could thus be checked during startup recovery.

I can see that we need to sync wal before write for certain changes, but
I don't see why we would currently need it for e.g. a heap insert, that
gets a free slot.

Andreas

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