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Re: Curious about dead rows.

From: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
To: Jean-David Beyer <jeandavid8(at)verizon(dot)net>
Cc: pgsql performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Curious about dead rows.
Date: 2007-11-10 18:51:19
Message-ID: 20071110105119.35346a29@scratch (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hash: SHA1

On Sat, 10 Nov 2007 13:38:23 -0500
Jean-David Beyer <jeandavid8(at)verizon(dot)net> wrote:

> Tom Lane wrote:
> > Jean-David Beyer <jeandavid8(at)verizon(dot)net> writes:
> >> I am doing lots of INSERTs on a table that starts out empty (I did
> >> a TRUNCATE on it). I am not, AFAIK, doing DELETEs or UPDATEs.
> >> Autovacuum is on. I moved logging up to debug2 level to see what
> >> was going on, and I get things like this:
> > 
> >>  "vl_as": scanned 3000 of 5296 pages, containing 232944 live rows
> >> and 1033 dead rows; 3000 rows in sample, 411224 estimated total
> >> rows
> > 
> >> A little later, it says:
> > 
> >> "vl_as": scanned 3000 of 6916 pages, containing 233507 live rows
> >> and 493 dead rows; 3000 rows in sample, 538311 estimated total rows
> > 
> > Well, *something* is doing deletes or updates in that table.  Better
> > look a bit harder at your application ...
> > 
> OK, you agree that if I am doing only INSERTs, that there should not
> be any dead rows. Therefore, I _must_ be doing deletes or updates.
> But the program is pretty simple, and I see no UPDATEs or DELETEs. I
> searched all the program source files (that contain none of them) and
> all the libraries I have written, and they have none either. Right
> now the programs are not to the state where UPDATEs or DELETEs are
> required (though they will be later). I am still developing them and
> it is easier to just restore from backup or start over from the
> beginning since most of the changes are data laundering from an
> ever-increasing number of spreadsheets.
> Am I right that TRUNCATE deletes all the rows of a table. They may
> then be still there, but would not autovacuum clean out the dead
> rows? Or maybe it has not gotten to them yet? I could do an explicit
> one earlier.

Truncate will not create dead rows. However ROLLBACK will. Are you
getting any duplicate key errors or anything like that when you insert?


Joshua D. Drake


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