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Re: crash-safe visibility map, take three

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: crash-safe visibility map, take three
Date: 2010-11-30 16:33:18
Message-ID: 27556.1291134798@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Oh, but it's worse than that.  When you XLOG a WAL record for each of
> those pages, you're going to trigger full-page writes for all of them.
>  So now you've turned 1GB of data to write into 2+ GB of data to
> write.

No, because only the first mod of each VM page would trigger a full page
write, at least assuming a reasonable ordering of the operations.

			regards, tom lane

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