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.Mamin@xxxxxxxxxxxx]
Sent: February 21, 2013 2:41 PM
To: Jeff Janes; Carlo Stonebanks
Cc: pgsql-performance@xxxxxxxxxxxxxx
Subject: AW: 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 |
