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.
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