| From: | "Mikheev, Vadim" <vmikheev(at)reveredata(dot)com> |
|---|---|
| To: | "'Manfred Koizar'" <mkoi-pg(at)aon(dot)at>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Nested transactions: low level stuff |
| Date: | 2003-03-19 18:08:45 |
| Message-ID: | 3705826352029646A3E91C53F7189E325187AD@sectorbase2.sectorbase.com |
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| Thread: | |
| Lists: | pgsql-hackers |
> 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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