Re: Slow planing...

After a couple of hours of trying different stuff, set enable_mergejoin =
off made the planning time look better: Planning time: 0.322 ms
Any ideas why this helps?

Regards,
Mladen Marinović

On Fri, Dec 6, 2019 at 11:14 AM Mladen Marinović <mladen(dot)marinovic(at)kset(dot)org>
wrote:

> Hi,
>
> Since this morning our system is running slower than usual. It turns out
> that some queries take a very long time to plan ( > 1 second). The problem
> occurs when joining bigger tables. There are no partition for the used
> tables. The problem has a time correlation with the last
> autovacuum/autoanalyse this morning, but manual vacuuming and analysing did
> not fix the problem.
>
> An example explain is:
>
> EXPLAIN ANALYSE
> SELECT 1
> FROM table_a a
> LEFT JOIN table_b bON b.a_id= a.id
> WHERE a.object_id=13
> AND a.timestamp<'2019-12-06'
> AND a.timestamp>'2019-12-03'
>
> Nested Loop Left Join (cost=1.28..18137.57 rows=6913 width=4) (actual
> time=0.043..90.016 rows=14850 loops=1)
> -> Index Scan using uq_object_id_timestamp on table_a a
> (cost=0.70..7038.49 rows=6913 width=8) (actual time=0.028..21.832
> rows=14850 loops=1)
> Index Cond: ((object_id = 13) AND (timestamp <
> '2019-12-06'::timestamp with time zone) AND (timestamp >
> '2019-12-03'::timestamp with time zone))
> -> Index Only Scan using table_b_a_id on table_b b (cost=0.57..1.60
> rows=1 width=8) (actual time=0.004..0.004 rows=0 loops=14850)
> Index Cond: (a_id = a.id)
> Heap Fetches: 0
> Planning time: 1908.550 ms
> Execution time: 91.004 ms
>
> The same query on a similar parallel system takes 5ms for planing (PG
> 9.4.).
>
> Is there a way to detect why the planing is taking this long?
>
> The database is a 9.6.1 with 32GB of shared_buffers, and 1GB of
> maintanance_work_mem, and machine CPU is below 80% all the time.
>
> Regards,
> Mladen Marinović
>