Re: [PATCH] Negative Transition Aggregate Functions (WIP)

Поиск
Список
Период
Сортировка
От David Rowley
Тема Re: [PATCH] Negative Transition Aggregate Functions (WIP)
Дата
Msg-id CAApHDvraf3mJ0n+JEOGdCBSiFdNGAWrUXtueziJvWpxtiRPW3A@mail.gmail.com
обсуждение исходный текст
Ответ на Re: [PATCH] Negative Transition Aggregate Functions (WIP)  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: [PATCH] Negative Transition Aggregate Functions (WIP)
Список pgsql-hackers
Дерево обсуждения
On Sun, Dec 15, 2013 at 3:08 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
I wrote:
> It's not so good with two-row windows though:

Actually, carrying that example a bit further makes the point even more
forcefully:

    Table       correct sum of          negative-transition
                this + next value       result
    1e20        1e20                    1e20 + 1 = 1e20
    1           1                       1e20 - 1e20 + 0 = 0
    0           0                       0 - 1 + 0 = -1
    0           1                       -1 - 0 + 1 = 0
    1

Those last few answers are completely corrupt.


I guess the answer for the people that complain about slowness could be that they create their own aggregate function which implements float4pl as the trans function and float4mi as the negative trans function. They can call it SUMFASTBUTWRONG() if they like. Perhaps it would be worth a note in the documents for this patch?

I've removed the negative trans function setups for float4 and float8 with SUM and AVG stuff in my working copy now.

As for numeric, I did start working on this just after I posted the original patch and before I saw your comment about it. I did end up making do_numeric_desperse() which was to be the reverse of do_numeric_accum(), but I got stuck on the equivalent of when do_numeric_accum() does mul_var(&X, &X, &X2, X.dscale * 2); 

If it is decided that we don't want to implement a negative trans function for numeric, then I guess I could leave in my trans function to allow users to create their own fast version, maybe?

Regards

David Rowley
 
                        regards, tom lane

В списке pgsql-hackers по дате отправления:

Предыдущее
От: Tatsuo Ishii
Дата:
Сообщение: Re: encoding name "SHIFT_JIS" is absent in chklocale.c
Следующее
От: Amit Kapila
Дата:
Сообщение: Re: Performance Improvement by reducing WAL for Update Operation