Andres Freund <andres@anarazel.de> writes:
> On 06/03/2009 06:21 PM, Tom Lane wrote:
>> I find this *really* hard to believe, because I've never seen the bitmap
>> support operations show up noticeably at all in profiles. What sort of
>> queries are you testing?
> Many left joins from one base relation to additional dimensions. All the
> dimensions are relatively complex views consisting out of multiple joins
> or subselects.
> Some correlated subqueries and some [NOT] EXISTS() are also included in
> some of the queries.
Hmmm, could you provide a complete test case? I'm thinking the behavior
might indicate some other performance issue, ie an unreasonable number
of bitmapset calls in some particular planning path.
There used to be some performance issues in this area back when we
represented sets of relids as integer Lists :-(, but the change to
bitmap sets pretty much stomped that. I'm just really surprised that
there would be anything measurable from changing the word width.
regards, tom lane