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Re: BUG #6167: pg_dump fails on table lock

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jesper Engman <jesper(at)engman(dot)net>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-bugs <pgsql-bugs(at)postgresql(dot)org>
Subject: Re: BUG #6167: pg_dump fails on table lock
Date: 2011-08-18 19:59:57
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
Jesper Engman <jesper(at)engman(dot)net> writes:
> I wonder if there is a small time span between when pg_dump starts and
> when all locks have been acquired that may be the problem (if a table
> is dropped during that time span). Is there such a small time of
> vulnerability?

Certainly.  pg_dump has to read pg_class to get the names of the tables,
and then try to lock each one.  If you drop a table during that window,
the lock command will fail.

The window is actually a bit longer than necessary in existing releases,
because pg_dump was doing some other stuff before it got around to
acquiring the locks.  I fixed that recently
but that patch hasn't made it to any released versions yet.  In any case
there's still a nonzero window.

> Excluding tables from the dump is not an option - that will be an
> incomplete backup.

Um ... if you know it's a transient table, why do you care about backing
it up?

			regards, tom lane

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