From: | "Zeugswetter Andreas SB SD" <ZeugswetterA(at)spardat(dot)at> |
---|---|
To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Bruce Momjian" <pgman(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Pre-page images in WAL |
Date: | 2001-11-27 10:04:42 |
Message-ID: | 46C15C39FEB2C44BA555E356FBCD6FA41EB437@m0114.s-mxs.net |
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Lists: | pgsql-hackers |
> In the brave new world of WAL, Postgres does not flush dirty buffers
to
> disk at transaction commit, relying on WAL to clean up if a database
or
> system failure occurs. If we don't log page images to WAL then I
think
> there's a hole here wherein a Postgres crash can lose data even though
> no failure of the surrounding OS occurs. Maybe it's safe, but I'm not
> convinced.
It should be (imho *is*) safe for heap pages, but not for index pages.
The reasoning for heap pages is, that the WAL code (pre page image)
already
coped with future heap page versions.
I would not expect it to work for index pages, since one "feature" of
the page images was to "undo" future index operations.
Andreas
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