On Thu, Jan 30, 2014 at 9:26 PM, Claudio Freire <klaussfre...@gmail.com> wrote: > Maybe not TOAST compression, but prefix compression.
I've thought about it as well. It's totally feasible, and likely worthwhile, but a little more tricky. > I've been wondering lately, whether a format change in the B-Tree > could be worth the effort: store values with prefix compression. It > would certainly help indexes of many kinds (text-valued, multi-column, > etc...). You can play tricks with the AM version, generally stored in the meta page, as in the recent commit 36a35c550ac114caa423bcbe339d3515db0cd957, without breaking pg_upgrade. Although a lot of these techniques may not actually require that kind of additional effort. > Now, I haven't checked if it's already done. Sorry if it is. I did > mock around btree code a lot and don't remember any of this, but I do > remember stuff that could be used to achieve it (specifically, all the > index-only-scan machinery, which allows for implicit info). I think it would make sense to do it on leaf pages, where there is frequently a lot of redundancy. The reason that I myself wouldn't do it first is that offhand I think that it'd be harder to come up with a very generic infrastructure to make it work across diverse types, and it isn't that useful where there isn't much redundancy in prefixes. The B-Tree code doesn't really know anything about the type indexed, and that's a useful property. But it's still definitely a useful goal. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
