Re: CTE optimization fence on the todo list?

On 05/03/2015 11:49 AM, Tom Lane wrote:
> Andrew Dunstan <andrew@dunslane.net> writes:
>> On 05/01/2015 07:24 PM, Josh Berkus wrote:
>>>> (A possible compromise position would be to offer a new GUC to
>>>> enable/disable the optimization globally; that would add only a reasonably
>>>> small amount of control code, and people who were afraid of the change
>>>> breaking their apps would probably want a global disable anyway.)
>> This could be a very bad, almost impossible to catch, behaviour break.
>> Even if we add the GUC, we're probably going to be imposing very
>> significant code audit costs on some users.
> On what grounds do you claim it'd be a behavior break?  It's possible
> that the subquery flattening would result in less-desirable plans not
> more-desirable ones, but the results should still be correct.
>
>             

I meant w.r.t. performance. Sorry if that wasn't clear.

cheers

andrew