Re: Why lots of temp schemas are being created

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Walter Coole <WCoole(at)aperiogroup(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>, Anirban Pal <anirban(dot)pal(at)newgen(dot)co(dot)in>, pgsql-novice(at)postgresql(dot)org, pgsql-general(at)postgresql(dot)org
Subject: Re: Why lots of temp schemas are being created
Date: 2010-02-04 02:35:50
Message-ID: 4928.1265250950@sss.pgh.pa.us
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Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Temp schemas are not destroyed on session shutdown; they are rather
> destroyed the next time the backend ID is reused. Normally that's not a
> problem, because a backend ID is reused pretty soon. It's only a
> problem when you use so high a backend ID due to high load, that a very
> long time passes before it's reused. Those temp tables linger and can
> cause Xid wraparound problems.

Not correct --- ordinarily temp tables are removed at backend shutdown.
The only time that wouldn't happen is in event of a backend crash. In
which case cleanup would happen at next use, as you describe.

The schemas are indeed left around, but they're empty in the normal case.

regards, tom lane

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