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Re: BUG #5946: Long exclusive lock taken by vacuum (not full)

From: Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Christopher Browne <cbbrowne(at)gmail(dot)com>, Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com>, pgsql-bugs <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: BUG #5946: Long exclusive lock taken by vacuum (not full)
Date: 2011-05-02 19:05:25
Message-ID: m2zkn4udmy.fsf@2ndQuadrant.fr (view raw or flat)
Thread:
Lists: pgsql-bugs
Greg Stark <gsstark(at)mit(dot)edu> writes:
> So is it ok for inserting one row to cause my table to grow by 90GB?
> Or should there be some maximum size increment at which it stops
> growing? What should that maximum be? What if I'm on a big raid system
> where that size doesn't even add a block to every stripe element?

I'd think that capping the idea to the segment size makes sense.

Also, what about having a background process (bgwriter or autovacuum
come to mind) doing the work, rather than the backend that happens to be
inserting the row?

It could send a message, and continue creating a newer 8kb block if the
background process has not yet extended the storage.  Also, to be safe I
guess we could arrange to have the new segment be created way before
reaching the very end of the relation (so that adding 8kb does not need
to create a new segment, so as to avoid a race condition with the
background process doing so itself).

Regards,
-- 
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support

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