pg.ddx.io  pgsql-hackers@postgresql.org mailing list archive  

help / color / mirror / Atom feed
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Michael Paquier <michael.paquier@gmail.com>
Cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: David Steele <david@pgmasters.net>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: Craig Ringer <craig@2ndquadrant.com>
Cc: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Subject: Re: Protect syscache from bloating with negative cache entries
Date: Fri, 01 Dec 2017 17:03:28 -0500
Message-ID: <3598.1512165808@sss.pgh.pa.us> (raw)
In-Reply-To: <20171201214534.dfp2sd427puislll@alap3.anarazel.de>
References: <20171031.184622.92520047.horiguchi.kyotaro@lab.ntt.co.jp>
	<CAB7nPqSGdesvS-odcP+RRJaBOssPazwKURf1GAUYZED4dKSmiQ@mail.gmail.com>
	<CA+TgmobPHMmQEEUFDU6XCSj5ArEfyagS1+wisJ8QAY+EsUNbxg@mail.gmail.com>
	<CAB7nPqQvbMc5Exx=Qfx=42Osntqrm-thLLt3wCiLvLaokcsg4Q@mail.gmail.com>
	<84820.1512015443@sss.pgh.pa.us>
	<CA+TgmoY9qNYtdx8xh463f=82NosFw4PgthFV4UeP7WhvWu_cbQ@mail.gmail.com>
	<85587.1512101829@sss.pgh.pa.us>
	<CA+TgmoYiztC-M7qf-LVGdG10qN2wvyVUgudtcyeMCkn0UATOqw@mail.gmail.com>
	<20171201213113.z4gbol66ipvg5b4o@alap3.anarazel.de>
	<3544.1512164423@sss.pgh.pa.us>
	<20171201214534.dfp2sd427puislll@alap3.anarazel.de>

Andres Freund <andres@anarazel.de> writes:
> On 2017-12-01 16:40:23 -0500, Tom Lane wrote:
>> I have no faith in either of these proposals, because they both assume
>> that the problem only arises over the course of many minutes.  In the
>> recent complaint about pg_dump causing relcache bloat, it probably does
>> not take nearly that long for the bloat to occur.

> To me that's a bit of a different problem than what I was discussing
> here.  It also actually doesn't seem that hard - if your caches are
> growing fast, you'll continually get hash-resizing of the
> various. Adding cache-pruning to the resizing code doesn't seem hard,
> and wouldn't add meaningful overhead.

That's an interesting way to think about it, as well, though I'm not
sure it's quite that simple.  If you tie this to cache resizing then
the cache will have to grow up to the newly increased size before
you'll prune it again.  That doesn't sound like it will lead to nice
steady-state behavior.

			regards, tom lane




view thread (272+ messages)  latest in thread

Message-ID: <3598.1512165808@sss.pgh.pa.us>
Permalink:  ../3598.1512165808@sss.pgh.pa.us/
Also on:    postgresql.org/message-id/3598.1512165808@sss.pgh.pa.us

 · 

reply
Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: pgsql-hackers@postgresql.org
  Cc: tgl@sss.pgh.pa.us, andres@anarazel.de, robertmhaas@gmail.com, michael.paquier@gmail.com, horiguchi.kyotaro@lab.ntt.co.jp, david@pgmasters.net, Jim.Nasby@bluetreble.com, craig@2ndquadrant.com
  Subject: Re: Protect syscache from bloating with negative cache entries
  In-Reply-To: <3598.1512165808@sss.pgh.pa.us>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox