On Tue, May 31, 2016 at 10:02 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> Now, this case is a little trickier. If we called it simply
>> parallel_degree rather than max_parallel_degree, then it would have
>> the same name as the reloption. But the reloption sets an exact
>> value, and the GUC sets a cap, which is a significant difference.
>
> The reloption does not set an exact value, according to the code:
>
> /*
> * Use the table parallel_degree, but don't go further than
> * max_parallel_degree.
> */
> parallel_degree = Min(rel->rel_parallel_degree, max_parallel_degree);
>
> although the existing documentation for it is so vague that you
> couldn't tell from that.
True, max_parallel_degree is an overriding limit. But the point is
that, without the reloption, you can't get lots of workers on a small
table. The reloption lets you do that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
