Horton

Re: Allowing parallel-safe initplans

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2023-04-19T02:42:08Z
Lists: pgsql-hackers 
On Tue, Apr 18, 2023 at 9:33 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Richard Guo <guofenglinux@gmail.com> writes:
> > 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.


Yeah, seems breaking the EXPLAIN output is inevitable if we move the
initPlans to the Gather node.  So maybe we need to keep the logic as in
v1 patch, i.e. avoid adding a Gather node when top_plan has initPlans.
If we do so, I wonder if we need to explain the potential wrong results
issue in the comments.

Thanks
Richard

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.