Re: Choosing parallel_degree

OK cool, thanks.

Can we remove the minimum size limit when the per table degree setting is
applied?

This would help for tables with 2 - 1000 pages combined with a high CPU
cost aggregate.

Cheers,

James Sewell,
PostgreSQL Team Lead / Solutions Architect
______________________________________

Level 2, 50 Queen St, Melbourne VIC 3000

*P *(+61) 3 8370 8000 *W* www.lisasoft.com *F *(+61) 3 8370 8099

On Sun, Mar 20, 2016 at 11:23 PM, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com
> wrote:

> On 18 March 2016 at 10:13, James Sewell <james(dot)sewell(at)lisasoft(dot)com> wrote:
> > This does bring up an interesting point I don't quite understand though.
> If I run parallel agg on a table with 4 rows with 2 workers will it run on
> two workers (2 rows each) or will the first one grab all 4 rows?
> It works on a per page basis, workers just each grab the next page to
> be scanned from a page counter that sits in shared memory, the worker
> just increments the page number, releases the lock on the counter and
> scans that page.
>
> See heap_parallelscan_nextpage()
>
> So the answer to your question is probably no. At least not unless the
> the page only contained 2 rows.
>
> --
> David Rowley http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>

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