> I see no concurrency problems.  If two or more backends visit the same
> tuple, they either write the same value to the same position which
> doesn't hurt, or one sees the other's changes which is a good thing.

AFAIR, on multi-CPU platforms it's possible that second transaction could
see COMMITTED state but still old (subtrans id) in xmin: it's not
guaranteed that changes made on CPU1 (V1 was changed first, then V2 was
changed) will appear at the same order on CPU2 (V2 may come first, then V1).

Vadim


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Wed, 19 Mar 2003 10:25:23 -0800
"Mikheev, Vadim" <vmikheev@reveredata.com>
Re: Nested transactions: low level stuff 