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Re: visibility maps and heap_prune

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, pgsql-hackers(at)momjian(dot)us, pgsql-hackers(at)postgresql(dot)org
Subject: Re: visibility maps and heap_prune
Date: 2010-02-27 14:40:17
Message-ID: 201002271440.o1REeHi12955@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Heikki Linnakangas wrote:
> Bruce Momjian wrote:
> > Pavan Deolasee wrote:
> >> On Fri, Feb 26, 2010 at 8:19 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> >>
> >>> Whatever happened to this?  It was in the first 9.0 commitfest but was
> >>> returned with feedback but never updated:
> >>>
> >>>
> >> Though Alex did some useful tests and review, and in fact confirmed that the
> >> VACUUM time dropped from 16494 msec to 366 msec, I somehow kept waiting for
> >> Heikki's decision on the general direction of the patch and lost interest in
> >> between. If we are still interested in this, I can work out a patch and
> >> submit for next release if not this.
> > 
> > OK, TODO added:
> > 
> > 	Have single-page pruning update the visibility map
> > 	* https://commitfest.postgresql.org/action/patch_view?id=75
> > 
> > Hopefully Heikki can comment on this.
> 
> I think I was worried about the possible performance impact of having to
> clear the bit in visibility map again. If you're frequently updating a
> tuple so that HOT and page pruning is helping you, setting the bit in
> visibility map seems counter-productive; it's going to be cleared soon
> again by another UPDATE. That's just a hunch, though. Maybe the overhead
> is negligible.

Should I remove the TODO item?  I updated the text to:

	Consider having single-page pruning update the visibility map

and added a URL to Heikki's new comment.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com
  PG East:  http://www.enterprisedb.com/community/nav-pg-east-2010.do
  + If your life is a hard drive, Christ can be your backup. +

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