Ajay P S <ajayps547@gmail.com> writes:
> I am pretty new to the Postgres code base. I would like to know the
> difference between HeapTupleData and TupleTableSlot structures.
HeapTupleData is just a pointer to a concrete tuple. It exists
mainly because it's often convenient to pass around the tuple's
logical location (table OID and t_self) along with the tuple.
The comments about it in htup.h tell you about all you need to
know.
TupleTableSlot is a more abstract concept, being a container
for a tuple that can be present in several different forms.
It can contain a concrete tuple (HeapTupleData), or a "virtual"
tuple that is just an array of Datum+isnull values. The executor
usually uses tuple slots to return tuples out of plan nodes;
they're not very common elsewhere.
regards, tom lane