A cool idea, but if I understand it correctly very specific and fussy. New DB's are spawned on this model, and all the developers would have to be aware of this non-standard behaviour, and DBA"s would have to create these indexes every month, for every DB (as the log tables are created every month). There are 89 session_id values in the January log (log_2013_01) so this would quickly get out of control. But - like I said - an interesting idea for more specific challenges.
From: Marc Mamin [mailto:m.ma...@intershop.de] Sent: February 21, 2013 2:41 PM To: Jeff Janes; Carlo Stonebanks Cc: pgsql-performance@postgresql.org Subject: AW: [PERFORM] Are bitmap index scans slow to start? >Rebuilding the index might help, as it would put all the leaf pages holding values for session_id=27 adjacent to each other, so they would read from disk faster. But with a name like >"session_id", I don't know how long such clustering would last though. >If I'm right about the index disk-read time, then switching to a plain index scan rather than a bitmap index scan would make no difference--either way the data has to come off the disk. >>I'd prefer a >>strategy that allowed fast performance the first time, rather than slow the >>first time and extremely fast subsequently. Hello, if the index is only used to locate rows for single session_id, you may consider split it in a set of partial indexes. e.g. create index i_0 on foo where session_id%4 =0; create index i_1 on foo where session_id%4 =1; create index i_2 on foo where session_id%4 =2; create index i_3 on foo where session_id%4 =3; (can be built in parallel using separate threads) Then you will have to ensure that all your WHERE clauses also contain the index condition: WHERE session_id = 27 AND session_id%4 =27%4 regards, Marc Mamin
