Hi Sylvain,
Might sound like a nasty question, and gurus will correct me if I'm wrong, but first thing to investigate is why the index is not used :
- You have 2/3 million rows per table so the planner should use the index. Seqscan is prefered for small tables.
- Maybe the WHERE clause of your DELETE statement doesn't make use of your start and end date columns ? If so, in which order ?
Please, provide with your Pg version and the table setup with the index.
Regards,
Sekine
2012/10/16 Sylvain CAILLET
<scaillet@alaloop.com>Hi to all,
I've got a trouble with some delete statements. My db contains a little more than 10000 tables and runs on a dedicated server (Debian 6 - bi quad - 16Gb - SAS disks raid 0). Most of the tables contains between 2 and 3 million rows and no foreign keys exist between them. Each is indexed (btree) on start_date / end_date fields (bigint). The Postgresql server has been tuned (I can give modified values if needed).
I perform recurrent DELETE upon a table subset (~1900 tables) and each time, I delete a few lines (between 0 and 1200). Usually it takes between 10s and more than 2mn. It seems to me to be a huge amount of time ! An EXPLAIN ANALYZE on a DELETE shows me that the planner uses a Seq Scan instead of an Index Scan. Autovaccum is on and I expect the db stats to be updated in real time (pg_stats file is stored in /dev/shm RAM disk for quick access).
Do you have any idea about this trouble ?