Re: Parallel Seq Scan

On Wed, Nov 11, 2015 at 11:29 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:
>
> Hi
>
> I have a first query
>
> I looked on EXPLAIN ANALYZE output and the numbers of filtered rows are
differen
>

Thanks for the report. The reason for this problem is that instrumentation
information from workers is getting aggregated multiple times. In
ExecShutdownGatherWorkers(), we call ExecParallelFinish where it
will wait for workers to finish and then accumulate stats from workers.
Now ExecShutdownGatherWorkers() could be called multiple times
(once we read all tuples from workers, at end of node) and it should be
ensured that repeated calls should not try to redo the work done by first
call.
The same is ensured for tuplequeues, but not for parallel executor info.
I think we can safely assume that we need to call ExecParallelFinish() only
when there are workers started by the Gathers node, so on those lines
attached patch should fix the problem.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com