Re: VACUUM (DISABLE_PAGE_SKIPPING on)

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: VACUUM (DISABLE_PAGE_SKIPPING on)
Date: 2020-11-19 21:02:43
Message-ID: CANP8+jKariOtUCB3=-kyBRXSfAfMhgvh-FSUr3CTh_2PgUMyCw@mail.gmail.com
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On Wed, 18 Nov 2020 at 02:04, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
>
> On 2020-Nov-17, Simon Riggs wrote:
>
> > As an additional optimization, if we do find a row that needs freezing
> > on a data block, we should simply freeze *all* row versions on the
> > page, not just the ones below the selected cutoff. This is justified
> > since writing the block is the biggest cost and it doesn't make much
> > sense to leave a few rows unfrozen on a block that we are dirtying.
>
> Yeah. We've had earlier proposals to use high and low watermarks: if any
> tuple is past the high watermark, then freeze all tuples that are past
> the low watermark. However this is ancient thinking (prior to
> HEAP_XMIN_FROZEN) and we don't need the low watermark to be different
> from zero, since the original xid is retained anyway.
>
> So +1 for this idea.

Patch to do this attached, for discussion.

--
Simon Riggs http://www.EnterpriseDB.com/

Attachment Content-Type Size
one_freeze_then_max_freeze.v5.patch application/octet-stream 2.8 KB

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