Re: Calculation of unused columns

Simon Riggs <simon@2ndQuadrant.com> writes:
> On Mon, 2009-10-19 at 13:43 -0400, Tom Lane wrote:
>> Simon Riggs <simon@2ndQuadrant.com> writes:
>>> I think we should have a 4th class of functions,
>>> volatile-without-side-effects (better name needed, obviously).
>>
>> What for?  There wouldn't be that many, I think.  random() and
>> clock_timestamp(), yeah, but most volatile user-defined functions
>> are either volatile-with-side-effects or misdeclared.

> Read only vs. read write?

Most read-only functions are stable or even immutable.  I don't say
that there's zero usefulness in a fourth class, but I do say it's
unlikely to be worth the trouble.  (The only reason it even came
up in this connection is that the default for user-defined functions
is "volatile" which would defeat this optimization ... but we could
hardly make the default anything else.)

            regards, tom lane