Re: A reloption for partitioned tables - parallel_workers

On Mon, 2021-03-01 at 17:39 +0900, Amit Langote wrote:
> > I am not sure.
> > IMO, for normal table, we use the following macro to get the parallel_workers:
> > ----------------------
> > /*
> > * RelationGetParallelWorkers
> > * Returns the relation's parallel_workers reloption setting.
> > * Note multiple eval of argument!
> > */
> > #define RelationGetParallelWorkers(relation, defaultpw) \
> > ((relation)->rd_options ? \
> > ((StdRdOptions *) (relation)->rd_options)->parallel_workers : (defaultpw))
> > ----------------------
> > Since we add new struct " PartitionedTableRdOptions ", It seems we need to get parallel_workers in different way.
> > Do we need similar macro to get partitioned table's parallel_workers ?
>
> Oh, you're right. The parallel_workers setting of a relation is only
> accessed through this macro, even for partitioned tables, and I can
> see that it is actually wrong to access a partitioned table's
> parallel_workers through this macro as-is. Although I hadn't tested
> that, so thanks for pointing that out.
>
> > Like:
> > #define PartitionedTableGetParallelWorkers(relation, defaultpw) \
> > xxx
> > (PartitionedTableRdOptions *) (relation)->rd_options)->parallel_workers : (defaultpw))
>
> I'm thinking it would be better to just modify the existing macro to
> check relkind to decide which struct pointer type to cast the value in
> rd_options to.

Here is an updated patch with this fix.

I added regression tests and adapted the documentation a bit.

I also added support for lowering the number of parallel workers.

Yours,
Laurenz Albe