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From: Tom Lane on 5 Aug 2010 14:53
Merlin Moncure <mmoncure(a)gmail.com> writes:
> On Thu, Aug 5, 2010 at 2:09 PM, Tom Lane <tgl(a)sss.pgh.pa.us> wrote:
>> I was not persuaded that there's a real bug in practice. �IMO, his
>> problem was a broken trigger not broken upsert logic. �Even if we
>> conclude this is unsafe, simply removing the example is of no help to
>> anyone.

> Well, the error handler is assuming that the unique_volation is coming
> from the insert made within the loop. This is obviously not a safe
> assumption in an infinite loop context.

Well, that's a fair point. Perhaps we should just add a note that if
there are any triggers that do additional inserts/updates, the exception
catcher had better check which table the unique_violation is being
reported for.

>> A more useful response would be to supply a correct example.

> Agree: I'd go further I would argue to supply both the 'safe' and
> 'high concurrency (with caveat)' way. I'm not saying the example is
> necessarily bad, just that it's maybe not a good thing to be pointing
> as a learning example without qualifications. Then you get a lesson
> both on upsert methods and defensive error handling (barring
> objection, I'll provide that).

Have at it.

regards, tom lane

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