Re: A GUC to prevent leader processes from running subplans?

On Tue, Oct 17, 2017 at 7:27 AM, Thomas Munro
<thomas.munro@enterprisedb.com> wrote:
> While testing parallelism work I've wanted to be able to prevent
> gather nodes from running the plan in the leader process, and I've
> heard others say the same.  One way would be to add a GUC
> "multiplex_gather", like in the attached patch.  If you set it to off,
> Gather and Gather Merge won't run the subplan unless they have to
> because no workers could be launched.  I thought about adding a new
> value for force_parallel_mode instead, but someone mentioned they
> might want to do this on a production system too and
> force_parallel_mode is not really for end users.  Better ideas?

I don't think overloading force_parallel_mode is a good idea, but
having some other GUC for this seems OK to me.  Not sure I like
multiplex_gather, though.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company