From: Martin Lesser <ml-pgsql@bettercom.de>
To: pgsql-performance@postgresql.org
Cc: Denis <denis.sailer@yellowbook.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Reasons and drawbacks for unused item pointers (was: Update using primary key slow)
Date: Thu, 27 Oct 2005 23:01:55 +0200
Message-ID: <87y84eznb0.fsf_-_@nb-aspire.bettercom.de> (raw)
In-Reply-To: <23322.1130442063@sss.pgh.pa.us>
References: <Xns96FC6CBBEC0CDdenissaileryellowboo@200.46.204.72>
<19722.1130429883@sss.pgh.pa.us>
<Xns96FC85EFAC158denissaileryellowboo@200.46.204.72>
<23322.1130442063@sss.pgh.pa.us>
Tom Lane <tgl@sss.pgh.pa.us> writes:
> Denis <denis.sailer@yellowbook.com> writes:
>> There were 1905028 unused item pointers.
> The "unused item pointers" number seems a bit high, but otherwise that
> looks pretty reasonable.
>
> Is it possible that the particular row you were updating has been
> updated quite a lot of times since the last vacuum? Or even quite
> a few times within a single transaction?
What causes this "unused item pointers" and which impact do they have
regarding performance?
If I understood your last posting correctly more than one update on a
single row between two vacuum's would i.e. result in one ore more
"unused item pointer". Does this slow down the vacuum process and/or
other processes? Until now I could not find an answer what this number
implies.
Regards
Martin
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To: pgsql-performance@postgresql.org
Cc: ml-pgsql@bettercom.de, denis.sailer@yellowbook.com
Subject: Re: Reasons and drawbacks for unused item pointers (was: Update using primary key slow)
In-Reply-To: <87y84eznb0.fsf_-_@nb-aspire.bettercom.de>
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