RE: Temporary tables prevent autovacuum, leading to XID wraparound

From: "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>
To: 'Michael Paquier' <michael(dot)paquier(at)gmail(dot)com>
Cc: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: RE: Temporary tables prevent autovacuum, leading to XID wraparound
Date: 2018-01-25 08:10:00
Message-ID: 0A3221C70F24FB45833433255569204D1F8A4F70@G01JPEXMBYT05
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> From: Michael Paquier [mailto:michael(dot)paquier(at)gmail(dot)com]
> As a superuser, DROP TABLE should work on the temporary schema of another
> session. Have you tried that to solve the situation?

Yes, we asked the customer to do that today. I think the customer will do in the near future.

> > * In this incident, autovacuum worker misjudged that
> > pg_temp_3.fetchchunks can't be deleted, although the creator
> > (pg_rewind) is no longer active. How can we delete orphan temporary
> > tables safely?
>
> As long as Postgres sees that its temporary schema is in use, it would think
> that the table is not orphaned. Another thing possible would be to have
> the session now holding this schema space to reuse fetchchunks so as things
> are reset.

I understood you suggested a new session which recycle the temp schema should erase the zombie metadata of old temp tables or recreate the temp schema. That sounds easy.

Regards
Takayuki Tsunakawa

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