Re: Query never completes with low work_mem (at least not within one hour)

2017-04-05 9:28 GMT+02:00 Daniel Westermann <
daniel(dot)westermann(at)dbi-services(dot)com>:

> >>what is result of EXPLAIN statement for slow and fast cases?
> >>
> >>regards
> >>
> >>Pavel
>
> For work_mem=32MB
>
> explain (analyze,verbose,buffers) select count(user_id) from users where
> user_id not in ( select id from ids);
> QUERY
> PLAN
> ------------------------------------------------------------
> --------------------------------------------------------------------------
> Aggregate (cost=83175.01..83175.02 rows=1 width=8) (actual
> time=7945.592..7945.593 rows=1 loops=1)
> Output: count(users.user_id)
> Buffers: shared read=29425
> -> Seq Scan on public.users (cost=16925.01..79425.01 rows=1500000
> width=4) (actual time=1928.665..5888.645 rows=2499999 loops=1)
> Output: users.user_id, users.username
> Filter: (NOT (hashed SubPlan 1))
> Rows Removed by Filter: 500001
> Buffers: shared read=29425
> SubPlan 1
> -> Seq Scan on public.ids (cost=0.00..14425.01 rows=1000001
> width=4) (actual time=11.111..868.382 rows=1000001 loops=1)
> Output: ids.id
> Buffers: shared read=4425
> Planning time: 187.396 ms
> Execution time: 7948.108 ms
> (14 rows)
>
> Time: 8244.493 ms
>
> For work_mem='16MB' it does not complete with analyze in on hour. For
> explain only:
>
> explain (verbose) select count(user_id) from users where user_id not in (
> select id from ids);
> QUERY
> PLAN
> ------------------------------------------------------------
> ----------------------------
> Aggregate (cost=38748092500.00..38748092500.01 rows=1 width=8)
> Output: count(users.user_id)
> -> Seq Scan on public.users (cost=0.00..38748088750.00 rows=1500000
> width=4)
> Output: users.user_id, users.username
> Filter: (NOT (SubPlan 1))
> SubPlan 1
> -> Materialize (cost=0.00..23332.01 rows=1000001 width=4)
> Output: ids.id
> -> Seq Scan on public.ids (cost=0.00..14425.01
> rows=1000001 width=4)
> Output: ids.id
> (10 rows)
>

There is a materialize op more

do you have a index on ids.id?

Pavel