On 5/1/13 4:57 AM, Fabien COELHO wrote:
> The use case of the option is to be able to generate a continuous gentle
> load for functional tests, eg in a practice session with students or for
> testing features on a laptop.
If you add this to
https://commitfest.postgresql.org/action/commitfest_view?id=18 I'll
review it next month. I have a lot of use cases for a pgbench that
doesn't just run at 100% all the time. I had tried to simulate
something with simple sleep calls, but I realized it was going to take a
stronger math basis to do the job well.
The situations where I expect this to be useful all require collecting
latency data and then both plotting it and doing some statistical
analysis. pgbench-tools computes worst-case and 90th percentile latency
for example, along with the graph over time. There's a useful concept
that some of the official TPC tests have: how high can you get the
throughput while still keeping the latency within certain parameters.
Right now we have no way to simulate that. What we see with write-heavy
pgbench is that latency goes crazy (>60 second commits sometimes) if all
you do is hit the server with maximum throughput. That's interesting,
but it's not necessarily relevant in many cases.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com
