(2014/03/15 15:53), Fabien COELHO wrote:
Hello Heikki,
A couple of comments:
* There should be an explicit "\setrandom ... uniform" option too, even though
you get that implicitly if you don't specify the distribution
Indeed. I agree. I suggested it, but it got lost.
* What exactly does the "threshold" mean? The docs informally explain that "the
larger the thresold, the more frequent values close to the middle of the
interval are drawn", but that's pretty vague.
There are explanations and computations as comments in the code. If it is about
the documentation, I'm not sure that a very precise mathematical definition will
help a lot of people, and might rather hinder understanding, so the doc focuses
on an intuitive explanation instead.
* Does min and max really make sense for gaussian and exponential
distributions? For gaussian, I would expect mean and standard deviation as the
parameters, not min/max/threshold.
Yes... and no:-) The aim is to draw an integer primary key from a table, so it
must be in a specified range. This is approximated by drawing a double value
with
the expected distribution (gaussian or exponential) and project it carefully
onto
integers. If it is out of range, there is a loop and another value is drawn. The
minimal threshold constraint (2.0) ensures that the probability of looping is
low.
* How about setting the variable as a float instead of integer? Would seem more
natural to me. At least as an option.
Which variable? The values set by setrandom are mostly used for primary keys. We
really want integers in a range.
Oh, I see. He said about documents.
+ Moreover, set gaussian or exponential with threshold interger value,
+ we can get gaussian or exponential random in integer value between
+ <replaceable>min</> and <replaceable>max</> bounds inclusive.
Collectry,
+ Moreover, set gaussian or exponential with threshold double value,
+ we can get gaussian or exponential random in integer value between
+ <replaceable>min</> and <replaceable>max</> bounds inclusive.
And I am going to fix the document more easily understanding for user.
Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
