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Re: Effects of cascading references in foreign keys

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Michael Fuhr <mike(at)fuhr(dot)org>, Bruno Wolff III <bruno(at)wolff(dot)to>, Martin Lesser <ml-pgsql(at)bettercom(dot)de>, Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Effects of cascading references in foreign keys
Date: 2007-09-26 08:21:12
Message-ID: 200709260821.l8Q8LCX05347@momjian.us (view raw or flat)
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Tom Lane wrote:
> Michael Fuhr <mike(at)fuhr(dot)org> writes:
> > On Sat, Oct 29, 2005 at 09:49:47AM -0500, Bruno Wolff III wrote:
> >> It looks like this feature was added last May, so I think it only applies
> >> to 8.1.
> 
> > Earlier versions appear to have at least some kind of optimization.
> 
> Yeah.  IIRC, for quite some time we've had tests inside the FK update
> triggers to not bother to search the other table if the key value hasn't
> changed.  What we did in 8.1 was to push that test further upstream, so
> that the trigger event isn't even queued if the key value hasn't
> changed.  (This is why you don't see the trigger shown as being called
> even once.)
> 
> Looking at this, I wonder if there isn't a bug or at least an
> inefficiency in 8.1.  The KeysEqual short circuit tests are still there
> in ri_triggers.c; aren't they now redundant with the test in triggers.c?
> And don't they need to account for the special case mentioned in the
> comment in triggers.c, that the RI check must still be done if we are
> looking at a row updated by the same transaction that created it?
> 
> 			regards, tom lane
> 
> ---------------------------(end of broadcast)---------------------------
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-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

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