Zeugswetter Andreas DCP SD wrote:
>
> > > 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 :-)

Well, if we need to scan the page quickly, having the bit, or a bit
combination that can only be the head, is helpful. What we usually do
is to combine a SITC bit with another bit that would never be set for
SITC, and that is the head, and you use macros to properly do tests. We
do this already in a number of cases.

--
Bruce Momjian bruce@momjian.us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +

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