Re: [HACKERS] copyObject() ? again

Tom Lane wrote:
> 
> More generally, however, I think that the very existence of the subPlan
> list is a bug.  It violates the notion that "pointer equality shouldn't
> matter" because the subPlan list *must* contain pointers to the actual
> member objects of a plan node's other substructure.
> 
> Moreover the subPlan list isn't even buying us much --- it wouldn't be
> that expensive to scan the substructure directly for plan-type nodes
> when necessary, exactly as SS_pull_subplan does.  Arguably this would
> take less time than is expended on memory allocation to build the
> explicit subPlan list.  So I suggest getting rid of the subPlan list
> entirely, rather than hacking on copyfuncs.

First, I apologize for any inconveniences in my implementation
of subselect. I agreed that current handling of subPlan lists
is bad, but parent plan need in this list for some initializations
and SUBPLAN_EXPR expressions inside parent plan also need in 
corresponding subPlan nodes (to execute them).

Well, this could be good solution:

1. Implement TopPlan node (upmost plan, we told about this and  seems that Jan wanted implement it).
2. Construct list of _all_ subPlan inside planner and  put this list into TopPlan node.
3. Put into Plan->subPlan list of _indices_ of subPlans used  in this Plan (indices in TopPlan->subPlan list).
4. Use indices in SUBPLAN_EXPR, istead of subPlan pointers.
5. Add to EState and ExprContext pointer to TopPlan->subPlan  list (to enable index --> node conversion in
ExecSubPlan()& ExecInitSubPlan()).  
 
Unfortunately, I missed this solution year ago -:(
And more of that, I have no time to implement this now, sorry.

> Plans also have an "initPlan" list that seems to have the same kind of
> problem.  I don't really understand the difference between initPlans

No problems here. As you see this list is just copied in copyfuncs
and this is ok.

> and subPlans --- plannodes.h says
>     List       *initPlan;        /* Init Plan nodes (un-correlated expr
>                                  * subselects) */
>     List       *subPlan;        /* Other SubPlan nodes */
> which doesn't convey a whole lot to my mind.  Does anyone understand
> why this distinction is made?  Is it really necessary?

Uncorrelated expression subqueries are processed differently
from all other subqueries.

Vadim