Re: pg_dump locks a table on dumping ... ?

From: "Marc G(dot) Fournier" <scrappy(at)postgresql(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: pg_dump locks a table on dumping ... ?
Date: 2004-03-24 02:57:14
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On Tue, 23 Mar 2004, Tom Lane wrote:

> "Marc G. Fournier" <scrappy(at)postgresql(dot)org> writes:
> > 'k, just had someone tell me that they believed that a pg_dump will lock a
> > table while the dump is happening ... my first thought/response was that
> > this would defeat the point of MVCC, no? And would make for a terrible
> > backup procedure on a very large database, since you'd just have made your
> > database useless for the duration ...
> > Can someone confirm/deny that the lock happens?
> pg_dump takes a reader's lock (AccessShareLock). This does not prevent
> reads or writes of the table. It does prevent dropping the table,
> making schema alterations to it (such as column add/drop), or anything
> else that wants an exclusive lock. I think that VACUUM FULL is the only
> thing particularly likely to cause a conflict in a running database.

Perfect, that makes sense ... thanks :)

Marc G. Fournier Hub.Org Networking Services (
Email: scrappy(at)hub(dot)org Yahoo!: yscrappy ICQ: 7615664

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