> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> "Rainer Mager" <rainer@vanten.com> writes:
> >> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> >> Hmm ... it's pretty unusual to see the index fetch portion of a
> bitmap
> >> scan take the bulk of the runtime. Usually that part is fast and
> where
> >> the pain comes is in fetching from the heap. I wonder whether that
> >> index has become bloated. How big are the table and the index
> >> physically? (Look at pg_class.relpages, or if you want a really
> >> accurate number try pg_relation_size().)
>
> > Can you give me some more info on how to look at these stats?
>
> Since you've got 8.3 it's easy: select pg_relation_size('tablename')
> (or indexname). The result is in bytes, so you might want to
> divide by 1K or 1M to keep the number readable.
Ok, nice and simple...I like it:
The result for the table ad_log, is 30,063 MB. The result for the index,
ad_log_date_all, is 17,151 MB. I guess this roughly makes sense since the
index is on 4 fields and the table only has 6 fields.
For the particular query I'm trying to optimize at the moment I believe I
should be able to use an index that references only 2 fields, which, I
imagine, should reduce the time needed to read it. I'll play with this a bit
and see what happens.
Any other suggestions?
--Rainer
