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

help / color / mirror / Atom feed

From: Tom Lane <tgl@sss.pgh.pa.us>
To: Russell Smith <mr-russ@pws.com.au>
Cc: Jean-David Beyer <jeandavid8@verizon.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: Curious about dead rows.
Date: Wed, 14 Nov 2007 17:46:24 -0500
Message-ID: <16999.1195080384@sss.pgh.pa.us> (raw)
In-Reply-To: <473B6C9D.1020804@pws.com.au>
References: <4735DBDB.5050208@verizon.net>
	<16627.1194714491@sss.pgh.pa.us>
	<4735FA9F.1080805@verizon.net>
	<b42b73150711131628q1469df3el6f557e10de07a05@mail.gmail.com>
	<473A5CC0.3060003@verizon.net>
	<b42b73150711131936l65b97b9ya7953383673b2710@mail.gmail.com>
	<473AE63D.7090305@verizon.net>
	<20071114152249.GA16041@crankycanuck.ca>
	<473B2A1F.30804@verizon.net>
	<473B6C9D.1020804@pws.com.au>

Russell Smith <mr-russ@pws.com.au> writes:
> It is possible that analyze is not getting the number of dead rows right?

Hah, I think you are on to something.  ANALYZE is telling the truth
about how many "dead" rows it saw, but its notion of "dead" is "not good
according to SnapshotNow".  Thus, rows inserted by a not-yet-committed
transaction would be counted as dead.  So if these are background
auto-analyzes being done in parallel with inserting transactions that
run for awhile, seeing a few not-yet-committed rows would be
unsurprising.

I wonder if that is worth fixing?  I'm not especially concerned about
the cosmetic aspect of it, but if we mistakenly launch an autovacuum
on the strength of an inflated estimate of dead rows, that could be
costly.

			regards, tom lane

view thread (41+ messages)  latest in thread

Message-ID: <16999.1195080384@sss.pgh.pa.us>
Permalink:  ../16999.1195080384@sss.pgh.pa.us/
Also on:    postgresql.org/message-id/16999.1195080384@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, mr-russ@pws.com.au, jeandavid8@verizon.net
  Subject: Re: Curious about dead rows.
  In-Reply-To: <16999.1195080384@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