Re: generic plans and "initial" pruning

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."

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