From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
Cc: | Hackers <pgsql-hackers(at)postgresql(dot)org>, heikki(at)enterprisedb(dot)com, itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp |
Subject: | Re: Remaining VACUUM patches |
Date: | 2007-04-18 22:12:54 |
Message-ID: | 20699.1176934374@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> The other patch was ITAGAKI Takahiro's patch to fix n_dead_tuples in
> pgstats after VACUUM when there is concurrent update activity. This
> patch is still on hold largely because the above patch would cause it to
> be a bit obsolete.
I objected (and still object) to this patch because it allows
n_dead_tuples to drift arbitrarily far away from reality --- a series of
vacuums will incrementally update it using probably-inaccurate deltas,
and there's nothing to ensure that the result converges rather than
diverging. In the real world it will result in n_dead_tuples becoming
less accurate, not more so.
There was some discussion about better ways to do it, IIRC, but no new
patch has been submitted.
regards, tom lane
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