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Re: VACUUM FULL needed sometimes to prevent transaction ID wraparound?

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Marinos Yannikos <mjy(at)geizhals(dot)at>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: VACUUM FULL needed sometimes to prevent transaction ID wraparound?
Date: 2006-08-22 19:19:53
Message-ID: 20060822191952.GG25475@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-performance
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/Tidbits/perf.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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