The following bug has been logged online:

Bug reference: 4059
Logged by: Mark Steben
Email address: msteben@autorevenue.com
PostgreSQL version: 8.2.5
Operating system: Linux redhat
Description: Vacuum full not always cleaning empty tables
Details:

I sent an email to 'pgsql-bugs@postgresql.org' entitled
'Possible bug with VACUUM FULL' and also an addendum
But neglected to also send this bug report form.
You can refer to those emails; in a nutshell, I have found that VACUUM FULL
will not clean dead tuples out of an empty table when other queries are
accessing the database. Test plans/scenarios are included.

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Mark Steben wrote:

> I sent an email to 'pgsql-bugs@postgresql.org' entitled
> 'Possible bug with VACUUM FULL' and also an addendum
> But neglected to also send this bug report form.
> You can refer to those emails; in a nutshell, I have found that VACUUM FULL
> will not clean dead tuples out of an empty table when other queries are
> accessing the database. Test plans/scenarios are included.

Yes, if other sessions have open transactions whose start time predate
the start time of the transaction that deletes of tuples, those tuples
cannot be removed by VACUUM. This is known and expected. Is this
what's happening here?

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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Mark Steben wrote:
> Yes, there are transactions that predate the start time of the vacuum full.
> However those transactions do not touch the table being vacuumed, they have
> nothing to do with it. Is this the expected behavior?

Yes. The system has no way to know that they will not examine the table
in the future, so it has to be conservative about what it removes.

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Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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Yes, there are transactions that predate the start time of the vacuum full.
However those transactions do not touch the table being vacuumed, they have
nothing to do with it. Is this the expected behavior?

Mark Steben
Senior Database Administrator
@utoRevenueT
A Dominion Enterprises Company
480 Pleasant Street
Suite B200
Lee, MA 01238
413-243-4800 Home Office
413-243-4809 Corporate Fax
msteben@autorevenue.com

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-----Original Message-----
From: Alvaro Herrera [mailto:alvherre@commandprompt.com]
Sent: Tuesday, March 25, 2008 9:24 PM
To: Mark Steben
Cc: pgsql-bugs@postgresql.org
Subject: Re: [BUGS] BUG #4059: Vacuum full not always cleaning empty tables

Mark Steben wrote:

> I sent an email to 'pgsql-bugs@postgresql.org' entitled
> 'Possible bug with VACUUM FULL' and also an addendum
> But neglected to also send this bug report form.
> You can refer to those emails; in a nutshell, I have found that VACUUM
FULL
> will not clean dead tuples out of an empty table when other queries are
> accessing the database. Test plans/scenarios are included.

Yes, if other sessions have open transactions whose start time predate
the start time of the transaction that deletes of tuples, those tuples
cannot be removed by VACUUM. This is known and expected. Is this
what's happening here?

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.


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Mark Steben wrote:

> [Mark Steben] Sorry for pressing the point, just making sure I
>
> understand what you're saying.
>
> So, the only way to ensure that a vacuum full will clean out
> an
>
> Empty table is to run it on a stand-alone server?

No -- the other alternative is to wait long enough for those other
transactions to go away.


--
Alvaro Herrera http://www.amazon.com/gp/registry/CTMLCN8V17R4
"La primera ley de las demostraciones en vivo es: no trate de usar el sistema.
Escriba un guión que no toque nada para no causar daños." (Jakob Nielsen)

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