Hello,

we're looking into the reason why we are getting warnings about
transaction ID wraparound despite a daily "vaccumdb -qaz". Someone is
claiming that VACUUM without FULL cannot reassign XIDs properly when
max_fsm_pages was set too low (it says so here too, but this is rather
old: http://www.varlena.com/GeneralBits/T....html#maxfsmp). Is
this true, or do we have a different issue here? We're using 8.1.3 with
a database generated on 8.1.3 (i.e. not migrated from 7.x or anything
like that).

Thanks,
Marinos

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TIP 5: don't forget to increase your free space map settings

Marinos Yannikos wrote:
> Hello,
>
> we're looking into the reason why we are getting warnings about
> transaction ID wraparound despite a daily "vaccumdb -qaz". Someone is
> claiming that VACUUM without FULL cannot reassign XIDs properly when
> max_fsm_pages was set too low (it says so here too, but this is rather
> old: http://www.varlena.com/GeneralBits/T....html#maxfsmp). Is
> this true, or do we have a different issue here? We're using 8.1.3 with
> a database generated on 8.1.3 (i.e. not migrated from 7.x or anything
> like that).

It's not true. Having shortage of FSM entries will make you lose space,
but it will be able to recycle Xids anyway.

I guess your problem is that you're not vacuuming all databases for some
reason. I'd advise to lose the -q and make sure you're not redirecting
to somewhere you can't read the log; the read the log and make sure
everything is going fine.

What's the warning anyway? Does it say that wraparound point is
nearing, or does it merely say that it is on Xid <some number here> and
you don't know how far that number actually is?

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

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TIP 6: explain analyze is your friend

I would guess that you are not running vacuumdb as a user with permission to
vacuum the postgres or template1 databases. Try telling vacuumdb to log in
as postgres or whatever your superuser account is called.


> -----Original Message-----
> From: pgsql-performance-owner@postgresql.org
> [mailtogsql-performance-owner@postgresql.org] On Behalf Of
> Marinos Yannikos
> Sent: Tuesday, August 22, 2006 1:11 PM
> To: pgsql-performance@postgresql.org
> Subject: [PERFORM] VACUUM FULL needed sometimes to prevent
> transaction ID wraparound?
>
>
> Hello,
>
> we're looking into the reason why we are getting warnings about
> transaction ID wraparound despite a daily "vaccumdb -qaz". Someone is
> claiming that VACUUM without FULL cannot reassign XIDs properly when
> max_fsm_pages was set too low (it says so here too, but this
> is rather
> old:
> http://www.varlena.com/GeneralBits/T....html#maxfsmp). Is
> this true, or do we have a different issue here? We're using
> 8.1.3 with
> a database generated on 8.1.3 (i.e. not migrated from 7.x or anything
> like that).
>
> Thanks,
> Marinos
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
>


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TIP 2: Don't 'kill -9' the postmaster

On Tue, 2006-08-22 at 20:10 +0200, Marinos Yannikos wrote:
> Hello,
>
> we're looking into the reason why we are getting warnings about
> transaction ID wraparound despite a daily "vaccumdb -qaz". Someone is
> claiming that VACUUM without FULL cannot reassign XIDs properly when
> max_fsm_pages was set too low (it says so here too, but this is rather
> old: http://www.varlena.com/GeneralBits/T....html#maxfsmp). Is
> this true, or do we have a different issue here? We're using 8.1.3 with
> a database generated on 8.1.3 (i.e. not migrated from 7.x or anything
> like that).

Usually this is caused by either:
(1) You're not vacuuming as a superuser, so it's not able to vacuum
everything.
(2) You have a long-running transaction that never completed for some
strange reason.

Hope this helps,
Jeff Davis


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TIP 2: Don't 'kill -9' the postmaster

Hi, Jeff & all,

Jeff Davis wrote:


> (2) You have a long-running transaction that never completed for some
> strange reason.

I just asked myself whether a 2-phase-commit transaction that was
prepared, but never committed, can block vacuuming and TID recycling.

Markus

--
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf. | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

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TIP 4: Have you searched our list archives?

http://archives.postgresql.org

Markus Schaber wrote:
> I just asked myself whether a 2-phase-commit transaction that was
> prepared, but never committed, can block vacuuming and TID recycling.
>

Yes.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com


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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match