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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>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: crash-safe visibility map, take three
Date: 2010-12-01 16:43:39
Message-ID: 17527.1291221819@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Hmm, actually, if we're willing to believe PD_ALL_VISIBLE in the page 
> header over the xmin/xmax on the tuples, we could simply not bother 
> doing anti-wraparound vacuums for pages that have the flag set. I'm not 
> sure what changes that would require outside heapam.c, as we'd have to 
> be careful to not trust the xmin/xmax if the flag was set.

That seems pretty ugly/dangerous.  If we're going to try to do something
here, I much prefer Robert's approach of marking each tuple in the tuple
header.

			regards, tom lane

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