Re: SQL/MED - core functionality

Heikki Linnakangas <heikki.linnakangas@enterprisedb.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