Re: 'prepare' is not quite schema-safe

Vlad <marchenko(at)gmail(dot)com> writes:
> so is it possible that a successfully prepared (and possibly a couple
> of times already executed) query will be invalidated by postgresql
> for some reason (like lack of memory for processing/caching other
> queries)? Assuming that no database structure changes has been
> performed.

Well, that assumption is wrong to start with: what if the query plan
uses an index that someone else has chosen to drop? Or the plan
depends on an inlined copy of a SQL function that someone has since
changed? Or the plan was chosen on the basis of particular settings
of planner parameters like random_page_cost, but the user has changed
these via SET? (The last is a pretty close analogy to changing
search_path, I think.)

I am not claiming that the backend handles all these cases nicely
today: it certainly doesn't. But we understand in principle how
to fix these problems by invalidating plans inside the backend.
I don't see how the DBD::Pg driver can hope to deal with any of
these situations :-(

regards, tom lane