Re: pgbench throttling latency limit

On 09/05/2014 06:38 PM, Jan Wieck wrote:
> On 09/05/2014 10:12 AM, Fabien COELHO wrote:
>> Note that despite pg appaling latency performance, in may stay well over
>> the 90% limit, or even 100%: when things are going well a lot of
>> transaction run in about ms, while when things are going bad transactions
>> would take a long time (although possibly under or about 1s anyway), *but*
>> very few transactions are passed, the throughput is very small. The fact
>> that during 15 seconds only 30 transactions are processed is a detail that
>> does not show up in the metric.

Yeah, it makes much more sense to measure the latency from the
"scheduled" time than the actual time.

> I haven't used the real pgbench for a long time. I will have to look at
> your patch and see what the current version actually does or does not.
>
> What I have been using is a Python version of pgbench that I wrote for
> myself when I started learning that language. That one does record both
> values, the DB transaction latency and the client response time (time
> from the request being entered into the Queue until transaction commit).
> When I look at those results it is possible to have an utterly failing
> run, with <60% of client response times being within 2 seconds, but all
> the DB transactions are still in milliseconds.

I think we have to reconsider what we're reporting in 9.4, when --rate
is enabled, even though it's already very late in the release cycle.
It's a bad idea to change the definition of latency between 9.4 and 9.5,
so let's get it right in 9.4.

> As said, I'll have to take a look at it. Since I am on vacation next
> week, getting ready for my first day at EnterpriseDB, this may actually
> happen.

Oh, congrats! :-)

- Heikki