Re: Slow Delete : Seq scan instead of index scan

Hi Craig,

Here are the outputs :

flows=# explain analyze delete from agg_t377_incoming_a40_dst_net_f5 where start_date < 1346487911000;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------
Seq Scan on agg_t377_incoming_a40_dst_net_f5 (cost=0.00..34448.96 rows=657622 width=6) (actual time=3429.058..7135.901 rows=143 loops=1)
Filter: (start_date < 1346487911000::bigint)
Total runtime: 7136.191 ms
(3 rows)

flows=# \d agg_t377_incoming_a40_dst_net_f5
Table "public.agg_t377_incoming_a40_dst_net_f5"
Column | Type | Modifiers
-------------+--------+-----------
end_date | bigint |
dst_network | inet |
total_pkts | bigint |
total_bytes | bigint |
start_date | bigint |
total_flows | bigint |
Indexes:
"agg_t377_incoming_a40_dst_net_f5_end_date" btree (end_date)
"agg_t377_incoming_a40_dst_net_f5_start_date" btree (start_date)

Thanks for your help,

Sylvain
----- Mail original -----

> On 10/16/2012 03:50 PM, Sylvain CAILLET wrote:
> > 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.

> Can you post that (or paste to explain.depesz.com and link to it
> here)
> along with a "\d tablename" from psql?

> --
> Craig Ringer