Horton

Re: Speed up transaction completion faster after many relations are accessed in a transaction

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, "Tsunakawa, Takayuki" <tsunakawa.takay@jp.fujitsu.com>, "Imai, Yoshikazu" <imai.yoshikazu@jp.fujitsu.com>, Andres Freund <andres@anarazel.de>, Simon Riggs <simon@2ndquadrant.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2019-04-07T14:41:12Z
Lists: pgsql-hackers 
On Mon, 8 Apr 2019 at 02:36, David Rowley <david.rowley@2ndquadrant.com> wrote:
> > LockMethodLocalHash is special in that it predictably goes to empty
> > at the end of every transaction, so that de-bloating at that point
> > is a workable strategy.  I think we'd probably need something more
> > robust if we were trying to fix this generally for all hash tables.
> > But if we're going to go with the one-off hack approach, we should
> > certainly try to keep that hack as simple as possible.
>
> As cheap as possible sounds good, but I'm confused at why you think
> the table will always be empty at the end of transaction. It's my
> understanding and I see from debugging that session level locks remain
> in there. If I don't copy those into the new table they'll be lost.

Or we could just skip the table recreation if there are no
session-levels.  That would require calling hash_get_num_entries() on
the table again and just recreating the table if there are 0 locks.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. Reorder LOCALLOCK structure members to compact the size

  2. Be more careful to not lose sync in the FE/BE protocol.