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.marino...@kset.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 >
