On 1999-11-04, Holger Klawitter mentioned:
>
> By the way,
>
> I've created a secondary index on a large table in order to
> gain some speed (the index is not unique), but the "explain"
> did not report any change.
>
> What else do I have to do to actually *use* an index? The manual
> only tells how to create one.
In general, nothing.
But:
* Perhaps your table is not big enough so the optimizer doesn't deem the
index worth its while.
* Perhaps you haven't run vacuum analyze lately, so the optimizer doesn't
even know the table size and makes questionable decisions.
* Perhaps your query is formed in a way that disqualifies the use of
indices.
* Perhaps the way you formed your query confuses the parser/optimizer.
(There are several such "unfortunate circumstances"/bugs.)
* Finally: Perhaps the optimizer is really smarter than you.
> FAQ?
Definitely. Question 4.9.
-Peter
--
Peter Eisentraut Sernanders vaeg 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
