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

help / color / mirror / Atom feed

From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Kirkwood <markir@paradise.net.nz>
Cc: Jim C. Nasby <jnasby@pervasive.com>
Cc: Markus Schaber <schabi@logix-tt.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: merge>hash>loop
Date: Wed, 19 Apr 2006 01:25:28 -0400
Message-ID: <22250.1145424328@sss.pgh.pa.us> (raw)
In-Reply-To: <4445C0EC.2060407@paradise.net.nz>
References: <1145029009.3422.31.camel@spectre.intellivid.com>
	<10000.1145031205@sss.pgh.pa.us>
	<1145033149.3422.41.camel@spectre.intellivid.com>
	<11035.1145033929@sss.pgh.pa.us>
	<4444C4CF.2000106@logix-tt.com>
	<20060418215238.GK49405@pervasive.com>
	<19388.1145398946@sss.pgh.pa.us>
	<20060418231552.GN49405@pervasive.com>
	<4445C0EC.2060407@paradise.net.nz>

Mark Kirkwood <markir@paradise.net.nz> writes:
> Jim C. Nasby wrote:
>> Good point. :/ I'm guessing there's no easy way to see how many blocks
>> for a given relation are in shared memory, either...

> contrib/pg_buffercache will tell you this -

I think the key word in Jim's comment was "easy", ie, cheap.  Grovelling
through many thousands of buffers to count the matches to a given
relation doesn't sound appetizing, especially not if it gets done over
again several times during each query-planning cycle.  Trying to keep
centralized counts somewhere would be even worse (because of locking/
contention issues).

			regards, tom lane

view thread (16+ messages)  latest in thread

Message-ID: <22250.1145424328@sss.pgh.pa.us>
Permalink:  ../22250.1145424328@sss.pgh.pa.us/
Also on:    postgresql.org/message-id/22250.1145424328@sss.pgh.pa.us

copy link · copy postgr.es

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-performance@postgresql.org
  Cc: tgl@sss.pgh.pa.us, markir@paradise.net.nz, jnasby@pervasive.com, schabi@logix-tt.com
  Subject: Re: merge>hash>loop
  In-Reply-To: <22250.1145424328@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