> On 22 Jul 2018, at 05:45, David Rowley <david.rowley@xxxxxxxxxxxxxxx> wrote: > > On 21 July 2018 at 20:15, Didier Carlier <didier.carlier@xxxxxxxxxxx> wrote: >> explain select count(*) from calendar c1, calendar c2, measure m where >> c1.stddate='2015-01-01' and c2.stddate='2015-12-31' and m.fromdateid >=c1.calendarid and m.fromdateid < c2.calendarid; >> QUERY PLAN >> -------------------------------------------------------------------------------------------------------------- >> Aggregate (cost=5073362.73..5073362.74 rows=1 width=8) >> -> Nested Loop (cost=8718.47..4988195.81 rows=34066770 width=0) >> -> Index Scan using calendar_stddate_unique on calendar c2 (cost=0.28..2.30 rows=1 width=4) >> Index Cond: (stddate = '2015-12-31 00:00:00+01'::timestamp with time zone) >> -> Nested Loop (cost=8718.19..4647525.81 rows=34066770 width=4) >> -> Index Scan using calendar_stddate_unique on calendar c1 (cost=0.28..2.30 rows=1 width=4) >> Index Cond: (stddate = '2015-01-01 00:00:00+01'::timestamp with time zone) >> -> Bitmap Heap Scan on measure m (cost=8717.91..4306855.81 rows=34066770 width=4) >> Recheck Cond: ((fromdateid >= c1.calendarid) AND (fromdateid < c2.calendarid)) >> -> Bitmap Index Scan on idx_measure_fromdate (cost=0.00..201.22 rows=34072527 width=0) >> Index Cond: ((fromdateid >= c1.calendarid) AND (fromdateid < c2.calendarid)) >> >> Both queries return the same answers but I don't see why the second one doesn't use parallel query. > > You'd likely be better of writing the query as: > > select count(*) from measure where fromdateid >= (select calendarid > from calendar where stddate = '2015-01-01') and fromdateid < (select > calendarid from calendar where stddate = '2015-12-31'); > > The reason you get the poor nested loop plan is that nested loop is > the only join method that supports non-equijoin. It doesn’t use a parallel query but It’s faster indeed, (~12 sec vs 9sec), thanks for the info. > > Unsure why you didn't get a parallel plan. Parallel in pg10 supports a > few more plan shapes than 9.6 did. Unsure what version you're using. It’s on 10.3 which is the latest available package prebuilt for SmartOS
