Horton

Re: [PROPOSAL] Use SnapshotAny in get_actual_variable_range

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>, Dmitriy Sarafannikov <dsarafannikov@yandex.ru>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Borodin Vladimir <root@simply.name>, Хомик Кирилл <khomikki@yandex-team.ru>
Date: 2017-04-27T21:33:54Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2017-04-27 17:22:25 -0400, Tom Lane wrote:
>> How so?  Shouldn't the indexscan go back and mark such tuples dead in
>> the index, such that they'd be visited this way only once?  If that's
>> not happening, maybe we should try to fix it.

> One way that never happens is if you end up choosing bitmap index scans
> all the time...

What I'm thinking of is the regular indexscan that's done internally
by get_actual_variable_range, not whatever ends up getting chosen as
the plan for the user query.  I had supposed that that would kill
dead index entries as it went, but maybe that's not happening for
some reason.

			regards, tom lane

Commits

  1. Improve performance of get_actual_variable_range with recently-dead tuples.

  2. Use SnapshotDirty rather than an active snapshot to probe index endpoints.