[BUGS] BUG #8516: Calling VOLATILE from STABLE function

[dwayne]

The following bug has been logged on the website:

Bug reference:  8516
Logged by:  Dwayne Towell
Email address:  dwa...@docketnavigator.com
PostgreSQL version: 9.2.4
Operating system:   CentOS
Description:

Why doesn't PostgreSQL give a warning when calling a volatile function from
a stable function?


For example:
CREATE TABLE x (val double);


CREATE FUNCTION g() RETURNS boolean AS $$
INSERT INTO x SELECT rand() RETURNING val>0.5; 
$$ LANGUAGE SQL VOLATILE;


CREATE FUNCTION f() RETURNS boolean AS $$
SELECT g(); -- this is where the stability-violation happens
$$ LANGUAGE SQL STABLE; -- this is a lie


According to the documentation, f() should be marked VOLATILE also, since
calling f() produces side effects. PostgreSQL does not give a warning (or
better yet, an error); I think it should.
 




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Re: [BUGS] BUG #8516: Calling VOLATILE from STABLE function

[Dwayne Towell]

> According to the documentation, f() should be marked VOLATILE also, since
> calling f() produces side effects. PostgreSQL does not give a warning (or
> better yet, an error); I think it should.

I think the answer is that function authors are required to prevent
functions they mark as STABLE from calling VOLATILE functions.

--

I understand it's an error (at least usually), my question/issue is why does
PostgreSQL NOT give at least a warning when a programmer (probably
accidentally) calls a VOLATILE function in one that he has specifically
tagged as STABLE? The compiler has all the information to notify the
programmer of a mistake, but isn't. This violates a fundamental principle of
software engineering--take every opportunity to prevent errors.

Dwayne 



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