On Jan 26, 2006, at 4:44 PM, Tom Lane wrote:
"Eric B. Ridge" <ebr@xxxxxxxx> writes:
Outside of "VACUUM FREEZE", is there any way the "xmin" column in a
relation can change, assuming of course the tuple is never updated
again?
If the tuple lives long enough, VACUUM will change it to
FrozenTransactionId
eventually, even without the FREEZE option.
That's what I was afraid of. I've pondering making a "grouping"
column that gets set to "xmin" via an UPDATE trigger. At least I'd
have a constant value that would survive database dumps and reloads.
This seems OK as long as the transaction was fairly recent. Note that
you will need a fairly restrictive definition of "same transaction"
(no subtransactions).
I really need a way to create a unique identifier at the start of a
top-level transaction, and be able to use it via triggers and/or
column default values in that or its subtransactions.
Is there some kind of "TopXID" magic variable/function that I haven't
found in the documentation?
eric
