| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | James Sewell <james(dot)sewell(at)lisasoft(dot)com> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Choosing parallel_degree |
| Date: | 2016-03-15 03:14:51 |
| Message-ID: | CAKJS1f_gQUk7zWZdYDro4Q0eUY5ZuF56VvZKM7CFqieTA60pYA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 15 March 2016 at 15:24, James Sewell <james(dot)sewell(at)lisasoft(dot)com> wrote:
>
> I did want to test with some really slow aggs, but even when I take out the small table test in create_parallel_paths I can't seem to get a parallel plan for a tiny table. Any idea on why this would be David?
In the test program I attached to the previous email, if I change the
parallel_threshold = 1000; to be parallel_threshold = 1; then I get
the following output:
For 1 pages there will be 1 workers (rel size 0 MB, 0 GB)
For 4 pages there will be 2 workers (rel size 0 MB, 0 GB)
So I'm getting 2 workers for only 4 pages. I've not tested in
Postgres, but if you do this and: SET parallel_setup_cost = 0; then
I'd imagine it should generate a parallel plan.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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