Hi,
On 06/03/2009 06:21 PM, Tom Lane wrote:
> Andres Freund<andres@anarazel.de> writes:
>> When switching bitmapword and companions in bitmap.h to u64 and s64
>> respectively I get an improvement up to 15% in queries with 16+ joins.
> 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.
I tested by compiling with 64bit bitmaps and without by repeatedly just
changing those three definitions. I don't see how I could get false
results with that?
I guess the biggest advantage comes from less cache trashing?
Andres