Subject: Re: pg_dump restore time and Foreign Keys
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Decibel! <decibel@decibel.org>, Andrew Dunstan <andrew@dunslane.net>,
	Robert Treat <xzilla@users.sourceforge.net>, pgsql-hackers@postgresql.org
In-Reply-To: <19362.1213023432@sss.pgh.pa.us>
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Date: Mon, 09 Jun 2008 16:12:59 +0100
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On Mon, 2008-06-09 at 10:57 -0400, Tom Lane wrote:
> Decibel! <decibel@decibel.org> writes:
> > Actually, in the interest of stating the problem and not the  
> > solution, what we need is a way to add FKs that doesn't lock  
> > everything up to perform the key checks.
> 
> Ah, finally a useful comment.  I think it might be possible to do an
> "add FK concurrently" type of command that would take exclusive lock
> for just long enough to add the triggers, then scan the tables with just
> AccessShareLock to see if the existing rows meet the constraint, and
> if so finally mark the constraint "valid".  Meanwhile the constraint
> would be enforced against newly-added rows by the triggers, so nothing
> gets missed.  You'd still get a small hiccup in system performance
> from the transient exclusive lock, but nothing like as bad as it is
> now.  Would that solve your problem?

That's good, but it doesn't solve the original user complaint about
needing to re-run many, many large queries to which we already know the
answer.

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support