Re: Promise index tuples for UPSERT

On 7 October 2014 03:31, Peter Geoghegan <pg(at)heroku(dot)com> wrote:

>> It may be that people on reading this now believe Peter's HW locking
>> approach is the best. I'm happy to go with consensus.
>
> I bet you didn't think that you'd say that a week ago. :-)

You're right, because last week I thought heavyweight locking sucks
and I still think that; I haven't said it is the best.

What we've just discovered is that we're locking 100% of the time, but
its not needed in 99.9% of cases and is arguable in the 0.1% case -
not "required" at all.

The price of avoiding that rare and possibly erroneous condition seems
high to me.

Is there a way of detecting that we are updating a unique constraint
column and then applying the HW locking only in that case? Or can we
only apply locking when we have multiple unique constraints on a
table?
If so, I would withdraw any objection to the HW locking technique.

--
Simon Riggs http://www.2ndQuadrant.com/
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