Re: BUG #8598: Row count estimates of partial indexes

Marko Tiikkaja <marko@joh.to> writes:
> On 11/17/13 9:18 PM, Tom Lane wrote:
>> The long-term answer as far as Postgres is concerned is to learn about
>> cross-column correlations, but that's not happening in the near future.

> I'm completely clueless about how the planner works, but wouldn't it be
> easier to have some kind of separate stats for the conditions in partial
> indexes?  It seems better in all cases than trying infer the stats from
> cross-column correlations, even if we had that.

There's been some discussion of providing a way to hint to ANALYZE about
which combinations of columns are worth gathering cross-column statistics
for.  But partial index predicates seem like a pretty bad mechanism for
that.

            regards, tom lane