show random_page_cost ;
random_page_cost
------------------
4
(1 row)
2015-10-27 12:30 GMT+01:00 Alex Ignatov <a.ignatov@xxxxxxxxxxxxxx>:
What is yours random_page_cost parameter in postgres config?
On 27.10.2015 14:19, Bertrand Paquet wrote:
relname | n_live_tup | n_dead_tup | last_vacuum | last_autovacuum | last_analyze | last_autoanalyze
------------------------+------------+------------+-------------------------------+-------------------------------+-------------------------------+-------------------------------
external_sync_messages | 998105 | 11750 | 2015-10-26 20:15:17.484771+00 | 2015-10-02 15:04:25.944479+00 | 2015-10-26 20:15:19.465308+00 | 2015-10-22 12:24:26.947616+00
(1 row)
2015-10-27 12:17 GMT+01:00 Alex Ignatov <a.ignatov@xxxxxxxxxxxxxx>:
What is the result ofOn 27.10.2015 14:10, Bertrand Paquet wrote:
Yes, I have run VACUUM ANALYZE, no effect.
Bertrand
2015-10-27 12:08 GMT+01:00 Alex Ignatov <a.ignatov@xxxxxxxxxxxxxx>:
Hello, Bertrand!On 27.10.2015 12:35, Bertrand Paquet wrote:
Hi all,
We have a slow query. After analyzing, the planner decision seems to be discutable : the query is faster when disabling seqscan. See below the two query plan, and an extract from pg_stats.
Any idea about what to change to help the planner ?
An information which can be useful : the number on distinct value on organization_id is very very low, may be the planner does not known that, and take the wrong decision.
Regards,
Bertrand
# explain analyze SELECT 1 AS one FROM "external_sync_messages" WHERE "external_sync_messages"."organization_id" = 1612 AND ("external_sync_messages"."status" NOT IN ('sent_to_proxy', 'in_progress', 'ok')) AND "external_sync_messages"."handled_by" IS NULL LIMIT 1;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..12.39 rows=1 width=0) (actual time=232.212..232.213 rows=1 loops=1)
-> Seq Scan on external_sync_messages (cost=0.00..79104.69 rows=6385 width=0) (actual time=232.209..232.209 rows=1 loops=1)
Filter: ((handled_by IS NULL) AND (organization_id = 1612) AND ((status)::text <> ALL ('{sent_to_proxy,in_progress,ok}'::text[])))
Rows Removed by Filter: 600140
Planning time: 0.490 ms
Execution time: 232.246 ms
(6 rows)
# set enable_seqscan = off;
SET
# explain analyze SELECT 1 AS one FROM "external_sync_messages" WHERE "external_sync_messages"."organization_id" = 1612 AND ("external_sync_messages"."status" NOT IN ('sent_to_proxy', 'in_progress', 'ok')) AND "external_sync_messages"."handled_by" IS NULL LIMIT 1;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.42..39.88 rows=1 width=0) (actual time=0.030..0.030 rows=1 loops=1)
-> Index Scan using index_external_sync_messages_on_organization_id on external_sync_messages (cost=0.42..251934.05 rows=6385 width=0) (actual time=0.028..0.028 rows=1 loops=1)
Index Cond: (organization_id = 1612)
Filter: ((handled_by IS NULL) AND ((status)::text <> ALL ('{sent_to_proxy,in_progress,ok}'::text[])))
Planning time: 0.103 ms
Execution time: 0.052 ms
(6 rows)
# SELECT attname, inherited, n_distinct, array_to_string(most_common_vals, E'\n') as most_common_vals FROM pg_stats WHERE tablename = 'external_sync_messages' and attname IN ('status', 'organization_id', 'handled_by');
attname | inherited | n_distinct | most_common_vals
-----------------+-----------+------------+------------------
handled_by | f | 3 | 3 +
| | | 236140 +
| | | 54413
organization_id | f | 22 | 1612 +
| | | 287 +
| | | 967 +
| | | 1223 +
| | | 1123 +
| | | 1930 +
| | | 841 +
| | | 1814 +
| | | 711 +
| | | 1513 +
| | | 1794 +
| | | 1246 +
| | | 1673 +
| | | 1552 +
| | | 1747 +
| | | 2611 +
| | | 2217 +
| | | 2448 +
| | | 2133 +
| | | 1861 +
| | | 2616 +
| | | 2796
status | f | 6 | ok +
| | | ignored +
| | | channel_error +
| | | in_progress +
| | | error +
| | | sent_to_proxy
(3 rows)
# select count(*) from external_sync_messages;
count
--------
992912
(1 row)
May be statistics on external_sync_messages is wrong? i.e planner give us rows=6385 but seq scan give us Rows Removed by Filter: 600140
Maybe you should recalc it by VACUUM ANALYZE it?
--
Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
select relname,n_live_tup,n_dead_tup, last_vacuum, last_autovacuum, last_analyze, last_autoanalyze from pg_stat_user_tables where relname='external_sync_messages' ?
-- Alex Ignatov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
-- Alex Ignatov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
