From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200212062330.gB6NUDl20018@candle.pha.pa.us>
Subject: Re: Rules/Trigges Trade-offs
In-Reply-To: <200212061525.49284.josh@agliodbs.com>
To: josh@agliodbs.com
Date: Fri, 6 Dec 2002 18:30:13 -0500 (EST)
Cc: Jean-Luc Lachance <jllachan@nsd.ca>, pgsql-sql <pgsql-sql@postgresql.org>
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Josh Berkus wrote:
> 
> Bruce, Richard,
> 
> > Triggers are mostly for testing/modifying the row being
> > inserted/updated, while rules are better for affecting other rows or
> > other tables.
> 
> Hmmm.  Thought that there were also some other criteria:
> 
> 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.

> 
> 2) Only Rules can "DO INSTEAD"; thus, only Rules are good for defining 
> Read/Write views.

True.

> 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.

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