On Tue, Nov 28, 2017 at 1:13 AM, Jakub Glapa <jakub.gl...@gmail.com> wrote: > The queries are somehow special. > We are still using the old style partitioning (list type) but we abuse it a > bit when querying. > When querying a set of partitions instead of doing it via parent table we > stitch together the required tables with UNION ALL (this requires less > locking) and was more performant in our benchmark (the new native > partitioning might improve this but we didn't research that yet). > > The queries are in form of > SELECT col1,col2,col3 FROM > (SELECT * > FROM par1 > WHERE rangestart >= '2017-01-01 00:00:00.0' AND rangeend <= > '2017-11-26 23:59:59.999' > UNION ALL SELECT * > FROM par2 > WHERE rangestart >= '2017-01-01 00:00:00.0' AND rangeend <= > '2017-11-26 23:59:59.999' > UNION ALL SELECT * > FROM par2 > WHERE rangestart >= '2017-01-01 00:00:00.0' AND rangeend <= > '2017-11-26 23:59:59.999' > > WHERE rangestart >= '2017-01-01 00:00:00.0' AND rangeend <= > '2017-11-26 23:59:59.999' > > UNION ALL > ... > ) unionalias > WHERE .... > > > > and indeed the query planner shows the usage of Bitmap Heap Scan > .... > -> Subquery Scan on "*SELECT* 2" > (cost=3068.58..19793.94 rows=1 width=1284) > -> Gather (cost=3068.58..19793.93 > rows=1 width=5014) > Workers Planned: 2 > -> Parallel Bitmap Heap Scan > on par_6 (cost=2068.58..18793.83 rows=1 width=5014) > Recheck Cond: > <<CONDITION>> > Filter: <<CONDITION>> > -> BitmapAnd > (cost=2068.58..2068.58 rows=30955 width=0) > -> BitmapOr > (cost=999.30..999.30 rows=42989 width=0) > -> Bitmap > Index Scan on par_6_datasource (cost=0.00..990.21 rows=42922 width=0) > Index > Cond: ((datasource)::text = 'one'::text) > -> Bitmap > Index Scan on par_6_datasource (cost=0.00..4.30 rows=1 width=0) > Index > Cond: ((datasource)::text = 'two'::text) > -> Bitmap > Index Scan on par_6_datasource (cost=0.00..4.79 rows=67 width=0) > Index > Cond: ((datasource)::text = 'three'::text) > -> Bitmap Index > Scan on par_6_rangestart (cost=0.00..1069.02 rows=47564 width=0) > Index Cond: > (rangestart >= '2017-01-01 00:00:00+01'::timestamp with time zone) > -> Subquery Scan on "*SELECT* 3" > (cost=761.33..7944.99 rows=1 width=1086) > -> Bitmap Heap Scan on par_7 > (cost=761.33..7944.98 rows=1 width=4816) > Recheck Cond: > <<CONDITION>> > Filter: <<CONDITION>> > -> BitmapAnd > (cost=761.33..761.33 rows=7045 width=0) > -> Bitmap Index Scan on > par_7_rangestart (cost=0.00..380.35 rows=14942 width=0) > Index Cond: > (rangestart >= '2017-01-01 00:00:00+01'::timestamp with time zone) > -> BitmapOr > (cost=380.72..380.72 rows=12248 width=0) > -> Bitmap Index > Scan on par_7_datasource (cost=0.00..372.00 rows=12228 width=0) > Index Cond: > ((datasource)::text = 'one'::text) > -> Bitmap Index > Scan on par_7_datasource (cost=0.00..4.36 rows=10 width=0) > Index Cond: > ((datasource)::text = 'two'::text) > -> Bitmap Index > Scan on par_7_datasource (cost=0.00..4.36 rows=10 width=0) > Index Cond: > ((datasource)::text = 'three'::text) > > .... > > > In this particular query there were over _100_ partitions connected with the > UNION ALL operator.
Ah, so you have many Gather nodes under Append? That's one way to eat arbitrarily many DSM slots. We allow for 64 + 2 * max_backends. Does it help if you increase max_connections? I am concerned about the crash failure mode you mentioned in the first email though: we should always be able to handle that condition gracefully. -- Thomas Munro http://www.enterprisedb.com
