Re: generic plans and "initial" pruning

Thanks for taking a look.

On Mon, Aug 28, 2023 at 10:43 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Aug 11, 2023 at 9:50 AM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> > After removing the unnecessary cleanup code from most node types’ ExecEnd* functions, one thing I’m tempted to do is remove the functions that do nothing else but recurse to close the outerPlan, innerPlan child nodes. We could instead have ExecEndNode() itself recurse to close outerPlan, innerPlan child nodes at the top, which preserves the close-child-before-self behavior for Gather* nodes, and close node type specific cleanup functions for nodes that do have any local cleanup to do. Perhaps, we could even use planstate_tree_walker() called at the top instead of the usual bottom so that nodes with a list of child subplans like Append also don’t need to have their own ExecEnd* functions.
>
> I think 0001 needs to be split up. Like, this is code cleanup:
>
> - /*
> - * Free the exprcontext
> - */
> - ExecFreeExprContext(&node->ss.ps);
>
> This is providing for NULL pointers where we don't currently:
>
> - list_free_deep(aggstate->hash_batches);
> + if (aggstate->hash_batches)
> + list_free_deep(aggstate->hash_batches);
>
> And this is the early return mechanism per se:
>
> + if (!ExecPlanStillValid(estate))
> + return aggstate;
>
> I think at least those 3 kinds of changes deserve to be in separate
> patches with separate commit messages explaining the rationale behind
> each e.g. "Remove unnecessary cleanup calls in ExecEnd* functions.
> These calls are no longer required, because <reasons>. Removing them
> saves a few CPU cycles and simplifies planned refactoring, so do
> that."

Breaking up the patch as you describe makes sense, so I've done that:

Attached 0001 removes unnecessary cleanup calls from ExecEnd*() routines.

0002 adds NULLness checks in ExecEnd*() routines on some pointers that
may not be initialized by the corresponding ExecInit*() routines in
the case where it returns early.

0003 adds the early return mechanism based on checking CachedPlan
invalidation, though no CachedPlan is actually passed to the executor
yet, so no functional changes here yet.

Other patches are rebased over these. One significant change is in
0004 which does the refactoring to make the callers of ExecutorStart()
aware that it may now return with a partially initialized planstate
tree that should not be executed. I added a new flag
EState.es_canceled to denote that state of the execution to complement
the existing es_finished. I also needed to add
AfterTriggerCancelQuery() to ensure that we don't attempt to fire a
canceled query's triggers. Most of these changes are needed only to
appease the various Asserts in these parts of the code and I thought
they are warranted given the introduction of a new state of query
execution.

--
Thanks, Amit Langote
EDB: http://www.enterprisedb.com