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From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: Bruce Momjian <pgman@candle.pha.pa.us>,
 Jean-Luc Lachance <jllachan@nsd.ca>
Subject: Re: Rules/Trigges Trade-offs
Date: Fri, 6 Dec 2002 15:25:49 -0800
Cc: pgsql-sql <pgsql-sql@postgresql.org>
References: <200212061634.gB6GYbt02565@candle.pha.pa.us>
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Message-Id: <200212061525.49284.josh@agliodbs.com>


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 lar=
ge=20
secondary tables can be a bad idea (maybe this has changed?)

2) Only Rules can "DO INSTEAD"; thus, only Rules are good for defining=20
Read/Write views.

3) There are no AFTER Rules, making, for example, a rule with a table check=
 on=20
the new data impractical, so you'd want to use Triggers or Constraints

etc.

There are, IMHO, some things Rules are better for, and some things Triggers=
=20
are better for.   I tend to use all Triggers except for updatable views,=20
simply because using a mix of Rules and Triggers can be very hard to keep=
=20
track of, but YMMV.


--=20
-Josh Berkus
 Aglio Database Solutions
 San Francisco