From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200212070224.gB72OiM06066@candle.pha.pa.us>
Subject: Re: Rules/Trigges Trade-offs
In-Reply-To: <200212061554.07415.josh@agliodbs.com>
To: josh@agliodbs.com
Date: Fri, 6 Dec 2002 21:24:44 -0500 (EST)
Cc: Jean-Luc Lachance <jllachan@nsd.ca>, pgsql-sql <pgsql-sql@postgresql.org>
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Josh Berkus wrote:
> 
> Bruce,
> 
> > > 1) Rules can't use indexes to do their processing, so Rules which query 
> large 
> > > secondary tables can be a bad idea (maybe this has changed?)
> > 
> > I don't think this is true.  Rewrite is before optimizer so it should be
> > optimized just the same.
> 
> I was speaking if the Rule has to do a lookup on a 2nd table in the course of 
> its processing; it used to be that such a lookup could not use indexes 
> because Rules are pre-optimizer.   This could have changed since 7.1, though.

As I remember, the RULE is processed just like an ordinary query.  I
wasn't aware it was looking up anything.

> > > 3) There are no AFTER Rules, making, for example, a rule with a table 
> check on 
> > > the new data impractical, so you'd want to use Triggers or Constraints
> > 
> > We have changed ordering in 7.3 where I think INSERT rules are _after_
> > the insert.
> 
> How would that work?  What if I want to reject the insert?

Uh, good question.  I can't remember now what we re-ordered in 7.3, but
I thought it had to do with rules.

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