| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
| Cc: | "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>, "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Pavan Deolasee" <pavan(at)enterprisedb(dot)com>, "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: HOT patch, missing things |
| Date: | 2007-08-09 17:14:34 |
| Message-ID: | 17274.1186679674@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> I agree about the costs for evaluating the expressions. But a COLD update is
> certainly going to have to evaluate both expressions once. The only additional
> cost here is that HOT is going to have to evaluate the *old* expression as
> well. So it's at worst twice as expensive as a normal COLD update.
What's bothering me is the case where we evaluate the expression twice,
find it doesn't match, and fall through to the COLD update logic which
will do it a third time.
> I think I'm leaning towards doing a binary comparison of the
> parameters to the expressions.
Yeah, we could simply insist on no change to any column that's used by
any of the expressions. That would be cheap to test.
regards, tom lane
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