Re: Parallel INSERT (INTO ... SELECT ...)

On Fri, Oct 16, 2020 at 9:26 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
>
> Cool, let me try to explain my thoughts a bit more. The idea is first
> (in standard_planner) we check if there is any 'parallel_unsafe'
> function/expression (via max_parallel_hazard) in the query tree. If we
> don't find anything 'parallel_unsafe' then we mark parallelModeOk. At
> this stage, the patch is checking whether there is any
> 'parallel_unsafe' or 'parallel_restricted' expression/function in the
> target relation and if there is none then we mark parallelModeOK as
> true. So, if there is anything 'parallel_restricted' then we will mark
> parallelModeOK as false which doesn't seem right to me.
>
> Then later in the planner during set_rel_consider_parallel, we
> determine if a particular relation can be scanned from within a
> worker, then we consider that relation for parallelism. Here, we
> determine if certain things are parallel-restricted then we don't
> consider this for parallelism. Then we create partial paths for the
> relations that are considered for parallelism. I think we don't need
> to change anything for the current patch in these later stages because
> we anyway are not considering Insert to be pushed into workers.
> However, in the second patch where we are thinking to push Inserts in
> workers, we might need to do something to filter parallel-restricted
> cases during this stage of the planner.
>

Posting an updated Parallel INSERT patch which (mostly) addresses
previously-identified issues and suggestions.

More work needs to be done in order to support parallel UPDATE and
DELETE (even after application of Thomas Munro's combo-cid
parallel-support patch), but it is getting closer.

Regards,
Greg Nancarrow
Fujitsu Australia