Re: Life cycles of tuple descriptors

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.

But I guess, making the between-the-lines of the contract explicit,
if lookup_rowtype_tupdesc is contracted to give me a tupdesc that sticks
around for as long as I haven't called ReleaseTupleDesc, and it sometimes
elects to give me one for which ReleaseTupleDesc is a no-op, the contract
is still that the thing sticks around for (at least) as long as I haven't
done that.

Cool. :)

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.

Regards,
-Chap