Re: [PATCH] add --throttle to pgbench (submission 3)

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