Re: [COMMITTERS] pgsql: Avoid having vacuum set reltuples to 0 onnon-empty relations in

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От Vik Fearing
Тема Re: [COMMITTERS] pgsql: Avoid having vacuum set reltuples to 0 onnon-empty relations in
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Msg-id CAJguA1SRBxPVJEs3knUnpvRcgzLTsmf2+mSXC-oRhXZJn+5pgw@mail.gmail.com
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Ответ на [COMMITTERS] pgsql: Avoid having vacuum set reltuples to 0 on non-empty relationsin  (Andrew Gierth <rhodiumtoad@postgresql.org>)
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On Thu, Mar 16, 2017 at 11:39 PM, Andrew Gierth <rhodiumtoad@postgresql.org> wrote:
Avoid having vacuum set reltuples to 0 on non-empty relations in the
presence of page pins, which leads to serious estimation errors in the
planner.  This particularly affects small heavily-accessed tables,
especially where locking (e.g. from FK constraints) forces frequent
vacuums for mxid cleanup.

Fix by keeping separate track of pages whose live tuples were actually
counted vs. pages that were only scanned for freezing purposes.  Thus,
reltuples can only be set to 0 if all pages of the relation were
actually counted.

Backpatch to all supported versions.

Per bug #14057 from Nicolas Baccelli, analyzed by me.

Discussion: https://postgr.es/m/20160331103739.8956.94469@wrigleys.postgresql.org

Congrats on your first commit!

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