On Tue, Sep 26, 2017 at 5:41 PM, Tomasz Ostrowski <tometzky...@ato.waw.pl> wrote: > I've noticed that hash indexes can't currently (in PG10) be multicolumn. Are > they technically hard to implement or just nobody took such a feature? > > I think multicolumn hash indexes should help pretty significantly with > queries like: > - where username=? and user_post_id=? > - where client_id=? and period=? and invoice_number=? > etc. > > I imagine that calculating a multicolumn hash should be pretty > straightforward to implement - after hashing bytes of first column just keep > going and update the hash state with bytes of a second and subsequent > columns. And it should allow for faster (O(1), less IO) and much smaller > (better cached, less IO again) multicolumn indexes. Also in PG10 hash > indexes are WAL-logged and therefore much easier to work with. What do you > think?
I was just thinking the same thing today. I think it is a great idea, but I don't have time to do the work myself at the moment. I'd be happy to help review, though. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers