On Mon, Mar 31, 2014 at 6:37 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Claudio Freire <klaussfre...@gmail.com> writes: >> On Mon, Mar 31, 2014 at 6:21 PM, Robert Haas <robertmh...@gmail.com> wrote: >>> On Fri, Mar 28, 2014 at 11:30 AM, Alexander Korotkov >>> <aekorot...@gmail.com> wrote: >>>> after reading Heikki Linnakangas presentation about GIN from Nordic PGDay, >>>> I >>>> figure out that btree_gin became much more attractive. >>>> http://hlinnaka.iki.fi/presentations/NordicPGDay2014-GIN.pdf > >>> This is a mighty interesting presentation. Could the posting tree >>> compression described on the "posting tree page format" slides (pp. >>> 16-17, I think) be used for btree also? Would we get similar >>> benefits? How much more expensive are updates with the new system? > >> I'd believe so, but it can make updates quite complicated. > >> I was going to take a stab at prefix-compression in b-tree, I could >> explore delta compression of the tids as well. > > Prefix compression definitely seems like it could be a win thanks to > index ordering (although note that on little-endian machines, you need to > be careful about which end of an integer is the "prefix"). I'm pretty > dubious about tid deltas being useful for btree, though. GIN has the > luxury of being able to sort a lot of tids into tid order, btree doesn't.
You still have lots of natural correlation in many real-world cases. Still, I agree that the overhead of maintaining such delta-compressed tid list can (and probably will) outweight the advantage. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
