Re: gaussian distribution pgbench

On 03/17/2014 10:40 AM, KONDO Mitsumasa wrote:
> By the way, you seem to want to remove --gaussian=NUM and --exponential=NUM
> command options. Can you tell me the objective reason? I think pgbench is the
> benchmark test on PostgreSQL and default benchmark is TPC-B-like benchmark.
> It is written in documents, and default benchmark wasn't changed by my patch.
> So we need not remove command options, and they are one of the variety of
> benchmark options. Maybe you have something misunderstanding about my patch...

There is an infinite number of variants of the TPC-B test that we could
include in pgbench. If we start adding every one of them, we're quickly
going to have hundreds of options to choose the workload. I'd like to
keep pgbench simple. These two new test variants, gaussian and
exponential, are not that special that they'd deserve to be included in
the program itself.

pgbench already has a mechanism for running custom scripts, in which you
can specify whatever workload you want. Let's use that. If it's missing
something you need to specify the workload you want, let's enhance the
script language.

The features we're missing, which makes it difficult to write the
gaussian and exponential variants as custom scripts, is the capability
to create random numbers with a non-uniform distribution. That's the
feature we should include in pgbench.

(Actually, you could do the Box-Muller transformation as part of the
query, to convert the uniform random variable to a gaussian one. Then
you wouldn't need any changes to pgbench. But I agree that "\setrandom
... gaussian" would be quite handy)

- Heikki