Re: Parallel Foreign Scans - need advice - Mailing list pgsql-hackers

From Andres Freund
Subject Re: Parallel Foreign Scans - need advice
Date
Msg-id 20190515173420.l6eir73xevfv5gy4@alap3.anarazel.de
Whole thread Raw
In response to Re: Parallel Foreign Scans - need advice  (Korry Douglas <korry@me.com>)
Responses Re: Parallel Foreign Scans - need advice  (Korry Douglas <korry@me.com>)
List pgsql-hackers
Hi,

Don't top quote on these list...

On 2019-05-15 13:31:59 -0400, Korry Douglas wrote:
> Thanks for the quick answer Andres.  You’re right - it was parallel_tuple_cost that was getting in my way; my query
returnsabout 6 million rows  so I guess that can add up.
 
> 
> If I change parallel_tuple_scan from 0.1 to 0.0001, I get a parallel foreign scan.
> 
> With 4 workers, that reduces my execution time by about half.  

Then you probably need to adjust the scan costs you have.


> But, nworkers_launched is always set to 0 in
> InitializeDSMForeignScan(), so that won’t work.  Any other ideas?

At that state it's simply not yet known how many workers will be
actually launched (they might not start successfully or such). Why do
you need to know it there and not later?

- Andres



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