Re: [HACKERS] modeling parallel contention (was: Parallel Append implementation) - Mailing list pgsql-hackers

From David Rowley
Subject Re: [HACKERS] modeling parallel contention (was: Parallel Append implementation)
Date
Msg-id CAKJS1f-rFjZkYHDe1as2zuCxLTjN2i4-JCXHLuDZpCH6F6NkGw@mail.gmail.com
Whole thread Raw
In response to Re: [HACKERS] modeling parallel contention (was: Parallel Appendimplementation)  (Andres Freund <andres@anarazel.de>)
Responses Re: [HACKERS] modeling parallel contention (was: Parallel Appendimplementation)  (Andres Freund <andres@anarazel.de>)
List pgsql-hackers
On 5 May 2017 at 14:36, Andres Freund <andres@anarazel.de> wrote:
> I wonder how much doing the atomic ops approach alone can help, that
> doesn't have the issue that the work might be unevenly distributed
> between pages.

I wondered that too, since I though the barrier for making this change
would be lower by doing it that way.

I didn't manage to think of a way to get around the wrapping the
position back to 0 when synch-scans are involved.

i.e
parallel_scan->phs_cblock++;
if (parallel_scan->phs_cblock >= scan->rs_nblocks)
parallel_scan->phs_cblock = 0;

-- David Rowley                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services



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