Re: 16-bit page checksums for 9.2

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, david(at)fetter(dot)org, aidan(at)highrise(dot)ca, stark(at)mit(dot)edu, pgsql-hackers(at)postgresql(dot)org
Subject: Re: 16-bit page checksums for 9.2
Date: 2012-01-06 21:44:02
Message-ID: CA+TgmoamCfv6FdQu8BXFvOFngq8TeTDxRTGbrLeXaYXfby0iKw@mail.gmail.com
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On Fri, Jan 6, 2012 at 3:47 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> Since we ignore hints during HS anyway,

No, we don't. We need to ignore visibility map bits, but we need not
and do not ignore HEAP_XMIN_COMMITTED, HEAP_XMAX_COMMITTED, etc.

> not setting them seems OK if
> checksums defined. Or we can recommend that you don't use checksums on
> a standby. Whichever fits.
>
> Writing pages during recovery doesn't need WAL. If we crash, we replay
> using the already generated WAL.

Which is all fine, except when you start making changes that are not
WAL-logged. Then, you have the same torn page problem that exists
when you it in normal running.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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