Re: Parallel Seq Scan

On 16/11/15 12:05, Robert Haas wrote:
> On Fri, Nov 13, 2015 at 10:46 AM, Thom Brown <thom@linux.com> wrote:
>>>> And perhaps associated PIDs?
>>> Yeah, that can be useful, if others also feel like it is important, I can
>>> look into preparing a patch for the same.
>> Thanks.
> Thom, what do you think the EXPLAIN output should look like,
> specifically?  Or anyone else who feels like answering.
>
> I don't think it would be very useful to repeat the entire EXPLAIN
> output n times, once per worker.  That sounds like a loser.  But we
> could add additional lines to the output for each node, like this:
>
>   Parallel Seq Scan on foo  (cost=0.00..XXX rows=YYY width=ZZZ) (actual
> time=AAA..BBB rows=CCC loops=1)
>    Leader: actual time=AAA..BBB rows=CCC loops=1
>    Worker 0: actual time=AAA..BBB rows=CCC loops=1
>    Worker 1: actual time=AAA..BBB rows=CCC loops=1
>    Worker 2: actual time=AAA..BBB rows=CCC loops=1
>
> If "buffers" is specified, we could display the summary information
> after the Parallel Seq Scan as normal and then display an additional
> per-worker line after the "Leader" line and each "Worker N" line.  I
> think displaying the worker index is more useful than displaying the
> PID, especially if we think that a plan tree like this might ever get
> executed multiple times with different PIDs on each pass.
>
> Like?  Dislike?  Other ideas?
>
Possibly have an option to include the PID?

Consider altering the format field width of the Worker number (depending 
on the number of workers) so you don't get:   Worker 9 ...   Worker 10 ...
but something like   Worker  9 ...   Worker 10 ...



Cheers,
Gavin