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Re: crash-safe visibility map, take three

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: crash-safe visibility map, take three
Date: 2010-11-30 17:36:07
Message-ID: 29237.1291138567@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> On 30.11.2010 19:22, Tom Lane wrote:
>> But having said that, I wonder whether we need a full-page image for
>> a WAL-logged action that is known to involve only setting a single bit
>> and updating LSN.

> You have to write a full-page image if you update the LSN, because 
> otherwise the next update that comes along will not write a full page image.

Um.  Drat.  I was thinking about the replay side, where I think it would
actually work --- but you're right, it would break the logic on the
generation side.  Unless you want to put in some kind of flag saying
"this was only a visibility bit update, any bigger update still needs
to write an FPI".

			regards, tom lane

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