On Fri, 2003-09-05 at 08:29, Jan Wieck wrote:
> It was not meant against anyone in person and I agree that nested
> transactions and/or catchable exceptions and continuing afterwards is
> usefull and missing in PostgreSQL. What Stephan and Richard where
> actually discussing was more like emulating the REPLACE INTO, and I was
> responding to that.
>
> However, even with nested transactions and exceptions and all that, your
> problem will not be cleanly solvable. You basically have 2 choices,
> trying the INSERT first and if that fails with a duplicate key then do
> the UPDATE, or try the UPDATE first and if no rows got hit do an INSERT.
> Now if 2 concurrent transactions do try the UPDATE they can both not
> find the row and do INSERT - one has a dupkey error. But if you try to
> INSERT and get a duplicate key, in the time between you get the error
> and issue the UPDATE someone else can issue a DELETE - the row is gone
> and your UPDATE will fail.
SERIALIZABLE transactions will solve this.
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