Обсуждение: median and percentile function implementation
Hello
Three years ago we worked on implementation of median function. http://www.postgresql.org/message-id/AANLkTimRksUOgGsK7-gTXnvJJGL-1QvuqxidusZQwep6@mail.gmail.com
Ideas how to solve this task? Can we move forward in some points?
Regards
Pavel
Pavel
On 08/26/2013 02:39 PM, Pavel Stehule wrote: > Hello > > Three years ago we worked on implementation of median function. > > http://www.postgresql.org/message-id/AANLkTimRksUOgGsK7-gTXnvJJGL-1QvuqxidusZQwep6@mail.gmail.com > > > Can we implement this function now? > > There are a few opened questions: > > * immutable parameters of aggregate functions > > * effective implementation when data are in memory > > * effective implementation when data are out of memory > > * effective implementation for usage as window function - running median. > > Better than before, we can choose between hashing and sorting based > aggregation. But tuplesort implementation is not right for using as > window function. Second issue can be a not possible reusing of > tuplesort for more final functions - median, percentile in one query. > > Ideas how to solve this task? Can we move forward in some points? Take a look at the standard-compliant WITHIN GROUP that is currently in development for 9.4. http://www.postgresql.org/message-id/2b8b55b8ba82f83ef4e6070b95fb0cd0@news-out.riddles.org.uk -- Vik
Hello
very nice! I tested it and works very well.Pavel
2013/8/26 Vik Fearing <vik.fearing@dalibo.com>
Take a look at the standard-compliant WITHIN GROUP that is currently inOn 08/26/2013 02:39 PM, Pavel Stehule wrote:
> Hello
>
> Three years ago we worked on implementation of median function.
>
> http://www.postgresql.org/message-id/AANLkTimRksUOgGsK7-gTXnvJJGL-1QvuqxidusZQwep6@mail.gmail.com
>
>
> Can we implement this function now?
>
> There are a few opened questions:
>
> * immutable parameters of aggregate functions
>
> * effective implementation when data are in memory
>
> * effective implementation when data are out of memory
>
> * effective implementation for usage as window function - running median.
>
> Better than before, we can choose between hashing and sorting based
> aggregation. But tuplesort implementation is not right for using as
> window function. Second issue can be a not possible reusing of
> tuplesort for more final functions - median, percentile in one query.
>
> Ideas how to solve this task? Can we move forward in some points?
development for 9.4.
http://www.postgresql.org/message-id/2b8b55b8ba82f83ef4e6070b95fb0cd0@news-out.riddles.org.uk
--
Vik
On Mon, Aug 26, 2013 at 10:15 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote: > Hello > > very nice! I tested it and works very well. > > And I looking for implementation in core. > > Two notes: > > * should to support string_agg and array_agg > > Regards > > Pavel > > > > 2013/8/26 Vik Fearing <vik.fearing@dalibo.com> >> >> On 08/26/2013 02:39 PM, Pavel Stehule wrote: >> > Hello >> > >> > Three years ago we worked on implementation of median function. >> > >> > >> > http://www.postgresql.org/message-id/AANLkTimRksUOgGsK7-gTXnvJJGL-1QvuqxidusZQwep6@mail.gmail.com >> > >> > >> > Can we implement this function now? >> > >> > There are a few opened questions: >> > >> > * immutable parameters of aggregate functions >> > >> > * effective implementation when data are in memory >> > >> > * effective implementation when data are out of memory >> > >> > * effective implementation for usage as window function - running >> > median. >> > >> > Better than before, we can choose between hashing and sorting based >> > aggregation. But tuplesort implementation is not right for using as >> > window function. Second issue can be a not possible reusing of >> > tuplesort for more final functions - median, percentile in one query. >> > >> > Ideas how to solve this task? Can we move forward in some points? >> >> Take a look at the standard-compliant WITHIN GROUP that is currently in >> development for 9.4. >> >> http://www.postgresql.org/message-id/2b8b55b8ba82f83ef4e6070b95fb0cd0@news-out.riddles.org.uk >> >> -- >> Vik >> > Thanks a ton! We will definitely look at supporting at the two functions you mentioned. Regards, Atri -- Regards, Atri l'apprenant