| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Chetan Suttraway <chetan(dot)suttraway(at)enterprisedb(dot)com> |
| Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, Sam Wong <sam(at)hellosam(dot)net>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Index use difference betweer LIKE, LIKE ANY? |
| Date: | 2011-06-06 09:47:10 |
| Message-ID: | 4DECA21E.2090307@enterprisedb.com |
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| Lists: | pgsql-performance |
On 06.06.2011 12:43, Heikki Linnakangas wrote:
> Also, even when safe, it's not clear that the transformation is always a
> win. The left-hand expression could be expensive, in which case having
> to evaluate it multiple times could hurt performance. Maybe yo
Sorry, hit "send" too early.
Maybe you could put in some heuristic to only do the transformation when
the left-hand expression is cheap, or maybe use something like the
CaseTestExpr to avoid multiple evaluation and still use the OR form.
Also, if the array is very large, opening it into the OR form could
increase plan time substantially, so we'd probably only want to do it if
there's any Vars involved, and thus any chance of matching an index.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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