Re: why doesn't DestroyPartitionDirectory hash_destroy?

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Mar 14, 2019 at 3:13 AM Amit Langote
> <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> I'm curious why DestroyPartitionDirectory doesn't do
>> hash_destroy(pdir->pdir_hash)?

> What would be the point? It's more efficient to let context teardown
> take care of it.

Agreed, but the comments in this area are crap. Why doesn't
CreatePartitionDirectory say something like

* The object lives inside the given memory context and will be
* freed when that context is destroyed. Nonetheless, the caller
* must *also* ensure that (unless the transaction is aborted)
* DestroyPartitionDirectory is called before that happens, else
* we may leak some relcache reference counts.

It's completely not acceptable that every reader of this code should
have to reverse-engineer these design assumptions, especially given
how shaky they are.

There's an independent question as to whether the planner's use of
the feature is specifying a safe memory context. Has this code been
exercised under GEQO?

regards, tom lane