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Re: Pre-page images in WAL

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: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
> In the brave new world of WAL, Postgres does not flush dirty buffers
> disk at transaction commit, relying on WAL to clean up if a database
> system failure occurs.  If we don't log page images to WAL then I
> 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)
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.


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