El lun, 08-02-2016 a las 10:04 +0000, Gustav Karlsson escribió:
Additional information:
The problematic row has likely received many hot updates (100k+). Could this be a likely explanation for the high execution time?
Could you check if autovacuum is doing its job with this query:
select * from pg_stat_user_tables where relname='konto' , is it last_autovaccum and last_autoanalyze recent ?
if you don't reduce n_dead_tup in a short time after the bulk process of hot update, it will be a explanation, and also a "idle in transaction" connection could cause it.
Regards,
Gustav
Hi,
Question:
What may cause a primary key index to suddenly become very slow? Index scan for single row taking 2-3 seconds. A manual vacuum resolved the problem.
Background:
We have a simple table ‘KONTO’ with about 600k rows.
Column | Type | Modifiers
------------------------------+-----------------------------+---------------
id | bigint | not null
...
Indexes:
"konto_pk" PRIMARY KEY, btree (id)
...
Over the weekend we experienced that lookups using the primary key index (‘konto_pk’) became very slow, in the region 2-3s for fetching a single record:
QUERY PLAN
Index Scan using konto_pk on konto (cost=0.42..6.44 rows=1 width=164) (actual time=0.052..2094.549 rows=1 loops=1)
Index Cond: (id = 2121172829)
Planning time: 0.376 ms
Execution time: 2094.585 ms
After a manual Vacuum the execution time is OK:
QUERY PLAN
Index Scan using konto_pk on konto (cost=0.42..6.44 rows=1 width=164) (actual time=0.037..2.876 rows=1 loops=1)
Index Cond: (id = 2121172829)
Planning time: 0.793 ms
Execution time: 2.971 ms
So things are working OK again, but we would like to know what may cause such a degradation of the index scan, to avoid this happening again? (We are using Postgresql version 9.4.4)
Regards,
Gustav