|From:||Bruce Momjian <bruce(at)momjian(dot)us>|
|To:||Leonardo F <m_lists(at)yahoo(dot)it>|
|Subject:||Re: bitmap indexes - performance|
|Views:||Raw Message | Whole Thread | Download mbox|
Leonardo F wrote:
> Using as a starting point the old bitmap patch in:
> I re-applied and re-worked the patch to see what kind of improvements over
> btrees bitmaps actually provided.
> Using a 20M rows table of 10/100/1000 random values, I've found that:
> 1) bulk index creation time is roughly 6 times better
> 2) index size is 6-15 times smaller (depending on column cardinality)
> 3) there's almost no difference in query times (but I have to make more
> 4) I can't say anything about the insertion performance, but I guess
> bitmap will perform way worse than btree
> Are these improvements (index creation time, index size) worth enough
> to keep on working on this?
> I mean: given that bitmaps don't give any benefits in query times, but
> only benefits related to disk size and bulk index creation times, and
> will have horrible performance for insertions/deletions: would this job be
> In case it is: I will try to clean up the patch and post it...
> As a side note: I guess that most of the bitmap indexes performance
> improvements in the SELECT area are already implemented in postgres
> in the bitmapand/or and bitmap scan stuff? I couldn't find any docs that
> say that bitmap indexes are faster for selects, unless of course they
> are ANDed/ORed together (which is something postgres already does
> for regular btree indexes)
Great report, thanks. The other big problem with on-disk bitmap indexes
is removing expired values via vacuum.
+ None of us is going to be here forever. +
|Next Message||Robert Haas||2010-07-01 14:18:40||Re: Cannot cancel the change of a tablespace|
|Previous Message||Leonardo F||2010-07-01 13:23:49||bitmap indexes - performance|