Hello Heikki,
>> This patch extends pgbench expression with functions. Currently only one
>> "abs" function is added. The point is rather to bootstrap the
>> infrastructure for other functions (such as hash, random variants...) to
>> be added later.
>
> I think it would actually be good to add at least some of those other
> functions in the initial patch.
Hmmm, sure. I wanted some feedback on the "how" before doing that, hence
the infrastructure patch submitted with just one fonction. Obviously I can
expand, but before that any opinion on the "how"?
For instance I decided against having individual functions recognized by
the lexer, and to really have an infrastructure for storing, checking and
adding them without lex/yacc.
> The infrastructure that this patch adds only supports arguments with a
> single argument, so it won't get us very far.
> Also, will we need non-integer (e.g. string, numeric, whatever)
> arguments for the functions?
Maybe float *constants* for random exponential & gaussian.
> How about other datatypes for variables in general?
The point is not to develop another full language in pgbench. People can
do things with PL/pgSQL & server side if it must be really advanced, the
point is really to facilitate pgbench "simple" scripts.
> Perhaps not, or if we do that can be a separate patch, but it's
> something to keep in mind. The pgbench script language is evolving into
> a full-blown Turing-complete programming language...
The point is *NOT* to do that. For Turing, basically you would need while
or recursion & condition. Currently there is no such thing and not plan
for such thing, and I do not think it is desirable.
> As an initial list of functions, I'd suggest:
>
> abs(x)
This is the one included in the patch.
> min(x, y, ...)
> max(x, y, ...)
Hmm, varargs...
> random_uniform(min, max)
Ok. probably just "random"?
> random_gaussian(min, max, threshold)
> random_exponential(min, max, threshold)
Hmm, threshold is a float.
> As soon as we add more functions, the way they are documented needs to
> be reworked too; we'll need to add a table in the manual to list them.
Yep.
--
Fabien.
