Re: Very slow postgreSQL 9.3.4 query

["Burgess, Freddie" <FBurgess@xxxxxxxxxxxxxxx>]

I have a cron job that updates the statistics on the "doti_sensor_report" table on the first Saturday of every month. Do you think I should re-generate these statistics more often? This table receives streaming inserts to the volume of about 350 million tuples per-month.

I'll generate new stat's over the weekend, and then execute a new plan

thanks

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From: Victor Yegorov [vyegorov@xxxxxxxxx]
Sent: Friday, September 26, 2014 3:15 PM
To: Burgess, Freddie
Subject: Re: Very slow postgreSQL 9.3.4 query

2014-09-26 19:17 GMT+03:00 Burgess, Freddie <FBurgess@xxxxxxxxxxxxxxx>:

Performance data is included in the attachment, via EXPLAIN PLAN, query takes approx 6 minutes to return count to UI.
Amount of data processed is also included in the attachment, 185 million row partition.

It looks like your statistics are off:

-> Index Scan using idx_sensor_report_query_y2014m09 on doti_sensor_report_y2014m09 this__1 (cost=0.57..137498.17 rows=3883 width=0) (actual time=168.416..348873.308 rows=443542 loops=1)

Optimizer expects to find ~ 4k rows, while in reality there're 2 orders of magnitude more rows that matches the condition.

Perhaps BitmapIndexScan could be faster here.

--
Victor Y. Yegorov