On Wed, Aug 9, 2017 at 8:54 PM, Kuntal Ghosh <kuntalghosh.2...@gmail.com> wrote:
> On Wed, Aug 9, 2017 at 10:24 AM, Haribabu Kommi > <kommi.harib...@gmail.com> wrote: > > > > I tested the latest patch and the parallel plan is getting choose for > most > > of > > the init plans. > > > Thanks for testing. > > > For the following query the parallel plan is not chosen. The query > contains > > an init plan that refer the outer node. > > > > postgres=# explain analyze select * from t1 where t1.i in (select t2.i > from > > t2 where t1.k = (select max(k) from t3 where t3.i=t1.i)); > > QUERY PLAN > > ------------------------------------------------------------ > --------------------------------------------------------- > > Seq Scan on t1 (cost=0.00..22426.28 rows=448 width=12) (actual > > time=8.335..132.557 rows=2 loops=1) > > Filter: (SubPlan 2) > > Rows Removed by Filter: 894 > > SubPlan 2 > > -> Result (cost=16.27..31.26 rows=999 width=4) (actual > > time=0.146..0.146 rows=0 loops=896) > > One-Time Filter: (t1.k = $1) > > InitPlan 1 (returns $1) > > -> Aggregate (cost=16.25..16.27 rows=1 width=4) (actual > > time=0.145..0.145 rows=1 loops=896) > > -> Seq Scan on t3 (cost=0.00..16.25 rows=2 width=4) > > (actual time=0.131..0.144 rows=0 loops=896) > > Filter: (i = t1.i) > > Rows Removed by Filter: 900 > > -> Seq Scan on t2 (cost=16.27..31.26 rows=999 width=4) > (actual > > time=0.012..0.013 rows=10 loops=2) > > Planning time: 0.272 ms > > Execution time: 132.623 ms > > (14 rows) > > > An observation is that the filter at Result node can't be pushed down > to the sequential scan on t2 because the filter is on t1. So, it has > to scan the complete t2 relation and send all the tuple to upper node, > a worst case for parallelism. Probably, this is the reason the > optimizer doesn't pick parallel plan for the above case. > > Just for clarification, do you see any changes in the plan after > forcing parallelism(parallel_tuple_cost, parallel_setup_cost, > min_parallel_table_scan_size=0)? There is no plan change with parallel* GUC changes. Regards, Hari Babu Fujitsu Australia
