I agree with you that if we have to add a sort phase, there is additional
work and that work could be significant depending on the design we
choose, however without that, this patch can have impact on many kind
of workloads, even in your mail in one of the tests
("pgbench -M prepared -N -T 100 -j 2 -c 4 -P 1" over 32 runs (4 clients))
it has shown 20% degradation which is quite significant and test also
seems to be representative of the workload which many users in real-world
will use.
Yes, I do agree with the 4 clients, but I doubt that many user run their
application at maximum available throughput all the time (like always
driving foot to the floor). So for me throttled runs are more
representative of real life.
Now one can say that for such workloads turn the new knob to off, but
in reality it could be difficult to predict if the load is always moderate.
Hmmm. The switch says "I prefer stable (say latency bounded) performance",
if you run a web site probably you should want that.
Anyway, I'll look at sorting when I have some time.
--
Fabien.
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