Re: BUG #17330: EXPLAIN hangs and very long query plans

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От Strahinja Kustudić
Тема Re: BUG #17330: EXPLAIN hangs and very long query plans
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Msg-id CADKbJJUziW53FCNzMZSfDompyQ8aWF1ZJjjhy8OHPWJ0smWR5Q@mail.gmail.com
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Ответ на Re: BUG #17330: EXPLAIN hangs and very long query plans  (Peter Geoghegan <pg@bowt.ie>)
Ответы Re: BUG #17330: EXPLAIN hangs and very long query plans  (Pavel Stehule <pavel.stehule@gmail.com>)
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On Fri, Dec 10, 2021 at 2:36 AM Peter Geoghegan <pg@bowt.ie> wrote:
Sounds like a problem with get_actual_variable_range(), which can scan
indexes at plan time to determine minimum or maximum values.

This actually has been improved quite a bit since Postgres 10. So as
Jeff said, seems like you might benefit from upgrading to a newer
major version. v11 has improved things in this exact area.

On my Docker instance when I execute EXPLAIN it starts reading a lot of data. The indexes of the biggest table the query reads are 50GB, so my guess is that it reads those indexes.

I allowed EXPLAIN in Docker to finish and it took almost 500 seconds and it was reading data all the time. After I reindexed the biggest table, EXPLAIN finished instantly. Can the index corruption cause this?

Note that this started happening in production after we deleted a few million rows from the biggest table.

Regards,
Strahinja

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