Robert Haas wrote:

> I just want to point out that if we change #1, we're breaking
> postgresql.conf compatibility for, IMHO, not a whole lot of benefit.
> I'd just leave it alone.

We can add the old name as a synonym in guc.c to maintain compatibility.

> I would propose to call #2 max_parallel_workers and #3
> max_parallel_degree, which I think is clear as daylight, but since I
> invented all of these names, I guess I'm biased.

You are biased :-)

> In terms of forward-compatibility, one thing to note is that we
> currently have only parallel QUERY, but in the future we will no doubt
> also have parallel operations that are not queries, like VACUUM and
> CLUSTER and ALTER TABLE.  If we put the word "query" into the name of
> a GUC, we're committing to the idea that it only applies to queries,
> and that there will be some other limit for non-queries.  If we don't
> put the word query in there, we are not necessarily committing to the
> reverse, but we're at least leaning in that direction.  So far I've
> largely dodged having to make a decision about this, because talking
> about the degree of parallelism for CLUSTER makes just as much sense
> as talking about the degree of parallelism for a query, but we could
> also decide to have e.g. maintenance_parallel_degree instead of
> max_parallel_degree for such operations.  But as we commit to names
> it's something to be aware of.

This is a very good point.

I think parallel maintenance commands are going to require different
tuning than different queries, and I'd rather have separate parameters
for those things rather than force the same parameter being changed over
and over depending on what is the session going to execute next.

Also, I think your proposed change from "max" to "maintenance" does not
make much sense; I'd rather have max_maintenance_parallel_degree.

Álvaro Herrera      
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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