Re: Choosing parallel_degree

On 15 March 2016 at 15:24, James Sewell <james.sewell@lisasoft.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
Ican'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