"murphy pope" <pope_murphy(at)hotmail(dot)com> writes:
> Did I get (most or any of) this right?
Mostly. A couple of comments: HeapTupleSatisfies can do scankey testing
(that is, see whether columns satisfy "col op constant" conditions) in
addition to the time-qual checking you are thinking about. Also, the
time qual is defined by reference to a "snapshot" --- there is not
necessarily a unique notion of which tuples are good, even within a
single transaction. It all depends on the snapshot you use.
You can learn more about time qual testing by reading the comments in
src/backend/utils/time/tqual.c.
regards, tom lane