Re: Parallel Seq Scan - Mailing list pgsql-hackers

On Thu, Sep 17, 2015 at 6:10 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Sep 10, 2015 at 12:12 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>>> 2. I think it's probably a good idea - at least for now, and maybe
>>> forever - to avoid nesting parallel plans inside of other parallel
>>> plans.  It's hard to imagine that being a win in a case like this, and
>>> it certainly adds a lot more cases to think about.
>>
>> I also think that avoiding nested parallel plans is a good step forward.
>
> Doing that as a part of the assess parallel safety patch was trivial, so I did.
>

I tried with latest HEAD code, seems to be problem is present in other
scenarios.

postgres=# explain select * from tbl a where exists (select 1 from tbl
b where a.f1=b.f1 limit 0);                                     QUERY PLAN
--------------------------------------------------------------------------------------Funnel on tbl a
(cost=0.00..397728310227.27rows=5000000 width=214)  Filter: (SubPlan 1)  Number of Workers: 10  ->  Partial Seq Scan on
tbla  (cost=0.00..397727310227.27
 
rows=5000000 width=214)        Filter: (SubPlan 1)        SubPlan 1          ->  Limit  (cost=0.00..437500.00 rows=1
width=0)               ->  Seq Scan on tbl b  (cost=0.00..437500.00 rows=1 width=0)                      Filter: (a.f1
=f1)  SubPlan 1    ->  Limit  (cost=0.00..437500.00 rows=1 width=0)          ->  Seq Scan on tbl b
(cost=0.00..437500.00rows=1 width=0)                Filter: (a.f1 = f1)
 
(13 rows)

postgres=# explain analyze select * from tbl a where exists (select 1
from tbl b where a.f1=b.f1 limit 0);
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
LOG:  worker process: parallel worker for PID 8775 (PID 9121) exited
with exit code 1
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
LOG:  worker process: parallel worker for PID 8775 (PID 9116) exited
with exit code 1
LOG:  worker process: parallel worker for PID 8775 (PID 9119) exited
with exit code 1
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
LOG:  worker process: parallel worker for PID 8775 (PID 9117) exited
with exit code 1
LOG:  worker process: parallel worker for PID 8775 (PID 9114) exited
with exit code 1
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
LOG:  worker process: parallel worker for PID 8775 (PID 9118) exited
with exit code 1
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
CONTEXT:  parallel worker, pid 9115
STATEMENT:  explain analyze select * from tbl a where exists (select 1
from tbl b where a.f1=b.f1 limit 0);
LOG:  worker process: parallel worker for PID 8775 (PID 9115) exited
with exit code 1
LOG:  worker process: parallel worker for PID 8775 (PID 9120) exited
with exit code 1
ERROR:  badly formatted node string "SUBPLAN :subLinkType 0 :testexpr"...
CONTEXT:  parallel worker, pid 9115


Regards,
Hari Babu
Fujitsu Australia