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Re: Improvement of procArray.xmin for VACUUM

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Gregory Stark <stark(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Improvement of procArray.xmin for VACUUM
Date: 2007-03-27 02:12:39
Message-ID: 200703270212.l2R2CdJ10077@momjian.us (view raw or flat)
Thread:
Lists: pgsql-patches
Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > Gregory Stark wrote:
> >> I have a question about what would happen for a transaction running a command
> >> like COPY FROM. Is it possible it would manage to arrange to have no live
> >> snapshots at all? So it would have no impact on concurrent VACUUMs? What about
> >> something running a large pg_restore?
> 
> > Interesting idea.
> 
> Indeed.  Currently, COPY forcibly sets a snapshot on the off chance
> something will use it, but I could certainly see making that happen
> "lazily", ie not at all in the simple case.
> 
> pg_restore is probably a lost cause, at least if you are running it
> in single-transaction mode.  I guess there'd be tradeoffs as to whether
> to do that or not ...

The bottom line is that more optimizations for VACUUM dead tuple
identification are possible.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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