Re: Enabling parallelism for queries coming from SQL or other PL functions

On Thu, Mar 23, 2017 at 11:26 PM, Robert Haas <robertmhaas@gmail.com> wrote:

>
> The changes to the plpgsql code don't look so good to me.  The change
> to exec_stmt_return_query fixes the same bug that I mentioned in the
> email linked above, but only half of it -- it corrects the RETURN
> QUERY EXECUTE case but not the RETURN QUERY case.  And it's clearly a
> separate change; that part is a bug fix, not an enhancement.

My bad. Since, you have given this as a separate patch in the link
upthread, I suppose there's nothing expected from me regarding this
right now.

> Some of
> the other changes depend on whether we're in a trigger, which seems
> irrelevant to whether we can use parallelism. Even if the outer query
> is doing writes, we can still use parallelism for queries inside the
> trigger function if warranted.  It's probably a rare case to have
> queries inside a trigger that are expensive enough to justify such
> handling but I don't see the value of putting in special-case logic to
> prevent it.
>
Fixed. I confused it with not allowing parallel workers when update
command is in progress.

> I suspect that code fails to achieve its goals anyway.  At the top of
> exec_eval_expr(), you call exec_prepare_plan() and unconditionally
> pass CURSOR_OPT_PARALLEL_OK, so when that function returns, expr->plan
> might now be a parallel plan.  If we reach the call to
> exec_run_select() further down in that function, and if we happen to
> pass false, it's not going to matter, because exec_run_select() is
> going to find the plan already initialized.
>
True, fixed.
The attached patch is to be applied over [1].

[1]  https://www.postgresql.org/message-id/CA%2BTgmoZ_ZuH%2BauEeeWnmtorPsgc_SmP%2BXWbDsJ%2BcWvWBSjNwDQ%40mail.gmail.com
-- 
Regards,
Rafia Sabih
EnterpriseDB: http://www.enterprisedb.com/