Re: [HACKERS] Faster methods for getting SPI results
| От | Jon Nelson |
|---|---|
| Тема | Re: [HACKERS] Faster methods for getting SPI results |
| Дата | |
| Msg-id | CAKuK5J2JXi5tGe-XB6gt1PT=hwatWGPOhV2=-XP7sxRUL67gAw@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: [HACKERS] Faster methods for getting SPI results (Peter Eisentraut <peter.eisentraut@2ndquadrant.com>) |
| Список | pgsql-hackers |
On Thu, Mar 2, 2017 at 10:03 AM, Peter Eisentraut <peter.eisentraut@2ndquadrant.com> wrote:
-- On 12/20/16 23:14, Jim Nasby wrote:
> I've been looking at the performance of SPI calls within plpython.
> There's a roughly 1.5x difference from equivalent python code just in
> pulling data out of the SPI tuplestore. Some of that is due to an
> inefficiency in how plpython is creating result dictionaries, but fixing
> that is ultimately a dead-end: if you're dealing with a lot of results
> in python, you want a tuple of arrays, not an array of tuples.
There is nothing that requires us to materialize the results into an
actual list of actual rows. We could wrap the SPI_tuptable into a
Python object and implement __getitem__ or __iter__ to emulate sequence
or mapping access.
Python objects have a small (but non-zero) overhead in terms of both memory and speed. A built-in dictionary is probably one of the least-expensive (memory/cpu) choices, although how the dictionary is constructed also impacts performance. Another choice is a tuple.
Avoiding Py_BuildValue(...) in exchange for a bit more complexity (via PyTuple_New(..) and PyTuple_SetItem(...)) is also a nice performance win in my experience.
Jon
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