Re: BUG #13798: Unexpected multiple exection of user defined function with out parameters

On Tue, Dec 8, 2015 at 10:24 AM, David G. Johnston
<david.g.johnston@gmail.com> wrote:
> On Tue, Dec 8, 2015 at 9:08 AM, Kevin Grittner <kgrittn@gmail.com> wrote:

>> [...] * causes expansion to the following query:
>>
>> SELECT
>>     (reproducebehavior()).message1,
>>     (reproducebehavior()).message2,
>>     (reproducebehavior()).message3,
>>     (reproducebehavior()).message4;
>>
>> From that you can see why it is not surprising that the function is
>> executed once per OUT parameter, especially if it is VOLATILE.
>
> While you've explained how to see what is happening it doesn't remove
> the POLA violation that has occurred here.

I tend to think of x.* as being something that is resolved at parse
analysis time, before any consideration is given to how to execute;
thus, when x is a function I didn't find it at all astonishing that
it resolved as above.  If you think of * as a macro that expands in
the above manner before planning, the fact that it does not
optimize to a single call is not surprising for a VOLATILE
function; that is required behavior.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
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