Horton

Re: removal of dangling temp tables

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-12-14T17:26:58Z
Lists: pgsql-hackers

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On 2018-Dec-14, Robert Haas wrote:

> On Fri, Dec 14, 2018 at 11:29 AM Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:
> > I think the best way to fix this is to call RemoveTempRelations()
> > unconditionally at session start (without doing the rest of the temp
> > table setup, just the removal.)
> 
> That would certainly simplify things.  I think I thought about that as
> far back as a734fd5d1c309cc553b7c8c79fba96218af090f7 but it seemed
> like a significant behavior change and I wasn't sure that everyone
> would like it.  In particular, it adds overhead to backend startup
> that, in the case of a large temp schema, could be fairly long.

Hmm, I think in the case covered by your commit, that is a session that
crashes with a few thousands of temp tables, this new patch might cause
a failure to open a new session altogether.

Maybe it'd be better to change temp table removal to always drop
max_locks_per_transaction objects at a time (ie. commit/start a new
transaction every so many objects).

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Have DISCARD ALL/TEMP remove leftover temp tables

  2. Make autovacuum more selective about temp tables to keep

  3. Make autovacuum more aggressive to remove orphaned temp tables

  4. autovacuum: Drop orphan temp tables more quickly but with more caution.