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

On Wed, Dec 9, 2020 at 10:11 AM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
>
> On Wed, Dec 9, 2020 at 1:35 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> > Most of the code present in
> > v9-0001-Enable-parallel-SELECT-for-INSERT-INTO-.-SELECT.patch is
> > applicable for parallel copy patch also. The patch in this thread
> > handles the check for PROPARALLEL_UNSAFE, we could slightly make it
> > generic by handling like the comments below, that way this parallel
> > safety checks can be used based on the value set in
> > max_parallel_hazard_context. There is nothing wrong with the changes,
> > I'm providing these comments so that this patch can be generalized for
> > parallel checks and the same can also be used by parallel copy.
>
> Hi Vignesh,
>
> You are absolutely right in pointing that out, the code was taking
> short-cuts knowing that for Parallel Insert,
> "max_parallel_hazard_context.max_interesting" had been set to
> PROPARALLEL_UNSAFE, which doesn't allow that code to be generically
> re-used by other callers.
>

In v10-0003-Enable-parallel-INSERT-and-or-SELECT-for-INSERT-INTO,
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -2049,10 +2049,6 @@ heap_prepare_insert(Relation relation,
HeapTuple tup, TransactionId xid,
* inserts in general except for the cases where inserts generate a new
* CommandId (eg. inserts into a table having a foreign key column).
*/
- if (IsParallelWorker())
- ereport(ERROR,
- (errcode(ERRCODE_INVALID_TRANSACTION_STATE),
- errmsg("cannot insert tuples in a parallel worker")));

I think I have given a comment long back that here we can have an
Assert to check if it is a parallel-worker and relation has a
foreign-key and probably other conditions if possible. It is better to
protect such cases from happening due to any bugs. Is there a reason
you have not handled it?

[1] - https://www.postgresql.org/message-id/CAA4eK1KyftVDgovvRQmdV1b%3DnN0R-KqdWZqiu7jZ1GYQ7SO9OA%40mail.gmail.com

--
With Regards,
Amit Kapila.