Horton

Re: Allowing parallel-safe initplans

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2023-04-18T13:33:57Z
Lists: pgsql-hackers 
Richard Guo <guofenglinux@gmail.com> writes:
> On Mon, Apr 17, 2023 at 11:04 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I wondered about that too, but how come neither of us saw non-cosmetic
>> failures (ie, actual query output changes not just EXPLAIN changes)
>> when we tried this?

> Sorry I forgot to mention that I did see query output changes after
> moving the initPlans to the Gather node.

Hmm, my memory was just of seeing the EXPLAIN output changes, but
maybe those got my attention to the extent of missing the others.

> It seems that in this case the top_plan does not have any extParam, so
> the Gather node that is added atop the top_plan does not have a chance
> to get its initParam filled in set_param_references().

Oh, so maybe we'd need to copy up extParam as well?  But it's largely
moot, since I don't see a good way to avoid breaking the EXPLAIN
output.

			regards, tom lane

Commits

  1. Account for optimized MinMax aggregates during SS_finalize_plan.

  2. Add test case showing that commit d0d44049d fixed a live bug.

  3. Allow plan nodes with initPlans to be considered parallel-safe.

  4. Allow parallel workers to execute subplans.

  5. Mark a query's topmost Paths parallel-unsafe if they will have initPlans.