Re: [PGSQL 8.3.5] Use of a partial indexes

Reg Me Please wrote:
> Only one question remains in my mind:
>
> why the planner is not using the partial index?
>
> The partial index is covering 2 predicates out of the 3 used in the where
> condition. Actually there is a boolean flag (to exclude "disabled" rows),
> a timestamp (for row age) and an int8 (a FK to another table).
> The first two are in the partial index in order to exclude "disabled" and
> older rows. The int8 is the "random" key I mentioned earlier.
>
> So the WHERE condition reads like:
>
> flag AND tstz >= '2008-01-01'::timestamptz and thekey=42
>
> I can see in the EXPLAIN that there is no mention to the partial index.
> Please keep in mind that the table has 8+M rows, few of which are flagged,
> about 70% don't match the age limit and few dozens match the key.
> In my opinion the partial index should help a lot.
>
> --
> Fahrbahn ist ein graues Band
> weisse Streifen, grüner Rand
>
>
For an index to be used the where clause must match the index. As the
index gets more complicated its less likely to be used.

I have 5 indexes on one table to answer the 5 possible ways the where
clause can look like.