Horton

Re: generic plans and "initial" pruning

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Amit Langote <amitlangote09@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2022-02-14T20:17:48Z
Lists: pgsql-hackers 
On Sun, Feb 13, 2022 at 4:55 PM David Rowley <dgrowleyml@gmail.com> wrote:
> FWIW, that would remove the whole point in init run-time pruning.  The
> reason I made two phases of run-time pruning was so that we could get
> away from having the init plan overhead of nodes we'll never need to
> scan.  If we wanted to show the (never executed) scans in EXPLAIN then
> we'd need to do the init plan part and allocate all that memory
> needlessly.

Interesting. I didn't realize that was why it had ended up like this.

> I understood at the time it was just the EXPLAIN output that you had
> concerns with. I thought that was just around the lack of any display
> of the condition we used for pruning.

That was part of it, but I did think it was surprising that we didn't
print anything at all about the nodes we pruned, too. Although we're
technically iterating over the PlanState, from the user perspective it
feels like you're asking PostgreSQL to print out the plan - so it
seems weird to have nodes in the Plan tree that are quietly omitted
from the output. That said, perhaps in retrospect it's good that it
ended up as it did, since we'd have a lot of trouble printing anything
sensible for a scan of a table that's since been dropped.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Stamp 19beta1.

  2. Revert "Don't lock partitions pruned by initial pruning"

  3. Ensure first ModifyTable rel initialized if all are pruned

  4. Fix bug in cbc127917 to handle nested Append correctly

  5. Remove unstable test suite added by 525392d57

  6. Don't lock partitions pruned by initial pruning

  7. Fix an oversight in cbc127917 to handle MERGE correctly

  8. Track unpruned relids to avoid processing pruned relations

  9. Perform runtime initial pruning outside ExecInitNode()

  10. Move PartitionPruneInfo out of plan nodes into PlannedStmt

  11. Fix setrefs.c's failure to do expression processing on prune steps.

  12. Remove obsolete executor cleanup code

  13. Revert "Move PartitionPruneInfo out of plan nodes into PlannedStmt"

  14. Move PartitioPruneInfo out of plan nodes into PlannedStmt

  15. Refactor and cleanup runtime partition prune code a little

  16. Remove some unnecessary fields from Plan trees.

  17. Remove more redundant relation locking during executor startup.

  18. Shut down Gather's children before shutting down Gather itself.