Re: SQL/MED - core functionality

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> I left out some details on what exactly FdwPlan should contain and what
> it's lifecycle should be. I'm thinking that it should be allocated in
> the CurrentMemoryContext that's active when the FDW Plan routine is
> called, which would be the same context where we store all the Plan
> objects. It should not be modified after creation, so that it doesn't
> need to be copied when the ForeignScan is copied with copyObject(). It
> should not contain transient state information like connection objects,
> or references to a remotely prepared cursor etc. It must be possible to
> call BeginScan multiple times with the same FdwPlan object, so that it
> can be stored in a prepared plan that is executed multiple times.

The above statements seem mutually contradictory. In particular,
I think you're proposing that copyObject copy only a pointer and not the
whole plan tree when copying ForeignScan. That is entirely
unworkable/unacceptable: quite aside from the semantic ugliness, it will
fail altogether for cached plans.

regards, tom lane