Re: Life cycles of tuple descriptors

Chapman Flack <chap@anastigmatix.net> writes:
> On 12/14/21 20:02, Tom Lane wrote:
>> The API contract for lookup_rowtype_tupdesc specifies that you must "call
>> ReleaseTupleDesc or DecrTupleDescRefCount when done using the tupdesc".
>> It's safe to assume that the tupdesc will stick around as long as you
>> haven't done that.

> I think what threw me was having a function whose API contract mentions
> reference counts, but that sometimes gives me things that don't have them.

That's supposed to be hidden under ReleaseTupleDesc; you shouldn't have to
think about it.

> Oh, hmm, maybe one thing in that API comment ought to be changed. It says
> I must call ReleaseTupleDesc *or* DecrTupleDescRefCount. Maybe that dates
> from before the shared registry? ReleaseTupleDesc is safe, but anybody who
> uses DecrTupleDescRefCount on a lookup_rowtype_tupdesc result could be
> in for an assertion failure if a non-refcounted tupdesc is returned.

Yeah, I was just wondering the same.  I think DecrTupleDescRefCount
is safe if you know you are looking up a named composite type, but
maybe that's still too much familiarity with typcache innards.

            regards, tom lane