> > head of the chain yet. With an index scan, finding the head is
easy,
> > but for a sequential scan, it seems more difficult, and we don't
have
> > any free space in the tail of the chain to maintain a pointer to the
head.
>
> Thinking some more, there will need to be a bit to uniquely
> identify the head of a CITC.

I don't think so. It would probably be sufficient to impose an order on
the CITC.
e.g. the oldest tuple version in the CITC is the head.
(An idea just in case we can't spare a bit :-)

Andreas

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match