Re: Questions on 7.2.1 query plan choices

Curt Sampson wrote:

>
>>Curt Sampson's nearby remarks about partial indexes are not a bad
>>suggestion.
>
> I just tried this out, and the disk space savings alone were pretty
> stunning.  On a 300,000 row table with about 1750 TRUE values and
> the rest FALSE, the full index was over 5 MB and the partial was
> less than 50K.
>
> But it turns out that the analyzer's stats were good enough that
> it made little difference to performance. Once I analyzed the table,
> even with the full index postgres figured out that the index scan
> (estimating 1300 values, in this case) would be faster.
>
> So I guess it's key correlation thing that did it, or perhaps he
> just had not analzyed the table.


Interesting.  I analyzed immediately prior to running explain and the
queries, so that is not the source.  It is repeatable.

Ed