Leonardo F wrote: > Using as a starting point the old bitmap patch in: > > http://archives.postgresql.org/message-id/20081101000154.go27...@fune > > > 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 > tests) > 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 > worthed? > > 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. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + None of us is going to be here forever. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers