Re: [patch] bit XOR aggregate functions

On 3/7/21 10:53 AM, Pavel Stehule wrote:
> ne 7. 3. 2021 v 10:36 odesílatel Vik Fearing <vik@postgresfriends.org>
> napsal:
> 
>> On 3/6/21 9:06 PM, David G. Johnston wrote:
>>> On Saturday, March 6, 2021, David Fetter <david@fetter.org> wrote:
>>>
>>>>
>>>>>>     SELECT BIT_XOR(b ORDER BY a, c)...        /* works */
>>>>>>     SELECT BIT_XOR(b) OVER (ORDER BY a, c)... /* works */
>>>>>>     SELECT BIT_XOR(b) FROM...                 /* errors out */
>>>>>
>>>>>
>>>>> Why would such an error be necessary, or even desirable?
>>>>
>>>> Because there is no way to ensure that the results remain consistent
>>>> from one execution to the next without such a guarantee.
>>>>
>>>
>>> Numerous existing aggregate functions have this behavior.  Making those
>>> error isn’t an option.  So is making this a special case something we
>> want
>>> to do (and also maybe make doing so the rule going forward)?
>>
>> Aside from the fact that bit_xor() does not need this, I am opposed to
>> it in general.  It is not our job to make people write correct queries.
>>
> 
> I cannot agree with the last sentence. It is questions about costs and
> benefits, but good tool should to make warnings when users does some stupid
> things.
> 
> It is important at this time, because complexity in IT is pretty high, and
> a lot of users are not well trained (but well trained people can make
> errors too). And a lot of users have zero knowledge about technology, So
> when it is possible, and when it makes sense, then Postgres should be
> simple and safe. I think it is important for renome too. It is about costs
> and  benefits. Good reputation is a good benefit for us too. Ordered
> aggregation was designed for some purposes, and should be used, when it has
> sense.

How many cycles do you recommend we spend on determining whether  ORDER
BY a, b  is sufficient but  ORDER BY a  is not?

If we had an optimization_effort_level guc (I have often wanted that),
then I agree that this could be added to a very high level.  But we
don't, so I don't want any of it.
-- 
Vik Fearing