Jim Nasby <jnasby@pervasive.com> writes:
> Question: do we currently create new index entries even if the index
> key hasn't changed?
Yes.
> If so, what's the purpose of storing the CTID of
> the next version in the old version of the row?
So that UPDATE can always find the newest version of the row,
independently of what indexes exist or how it got to the row.
You may care to re-read the second paragraph here:
http://developer.postgresql.org/docs/postgres/transaction-iso.html#XACT-READ-COMMITTED
regards, tom lane