| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org>, Zeugswetter Andreas DCP SD <ZeugswetterA(at)spardat(dot)at>, Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Martijn van Oosterhout <kleptog(at)svana(dot)org>, Dann Corbit <DCorbit(at)connx(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Rick Gigger <rick(at)alpinenetworking(dot)com>, Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, josh(at)agliodbs(dot)com, pgsql-hackers(at)postgresql(dot)org, Jaime Casanova <systemguards(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Subject: | Re: MERGE vs REPLACE |
| Date: | 2005-11-18 15:34:35 |
| Message-ID: | 6410.1132328075@sss.pgh.pa.us |
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Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Oh, good point. I was thinking just about concurrent MERGEs. However,
> it is more complicated than that. By definitaion you can not see
> changes from other transactions while your statement is being run (even
> if you increment CommandCounter), so to be atomic, you would still see
> the row even though some other transaction had deleted it.
We would have to use the same semantics we use now for read-committed
UPDATE, that is look at the latest version of the row even though this
would not normally be visible to the transaction's snapshot.
In the case of a serializable transaction, no doubt we should fail if
any concurrent change actually happens.
regards, tom lane
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