Re: A reloption for partitioned tables - parallel_workers

On Tue, 2021-02-16 at 16:29 +0900, Amit Langote wrote:
> > I am +1 on allowing to override the degree of parallelism on a parallel
> > append. If "parallel_workers" on the partitioned table is an option for
> > that, it might be a simple solution. On the other hand, perhaps it would
> > be less confusing to have a different storage parameter name rather than
> > having "parallel_workers" do double duty.
> > Also, since there is a design rule that storage parameters can only be used
> > on partitions, we would have to change that - is that a problem for anybody?
>
> I am not aware of a rule that suggests that parallel_workers is always
> interpreted using storage-level considerations. If that is indeed a
> popular interpretation at this point, then yes, we should be open to
> considering a new name for the parameter that this patch wants to add.

Well, https://www.postgresql.org/docs/current/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS
says:

"Specifying these parameters for partitioned tables is not supported,
but you may specify them for individual leaf partitions."

If we re-purpose "parallel_workers" like this, we'd have to change this.

Then for a normal table, "parallel_workers" would mean how many workers
work on a parallel table scan. For a partitioned table, it determines
how many workers work on a parallel append.

Perhaps that is similar enough that it is not confusing.

Yours,
Laurenz Albe