Re: Faster methods for getting SPI results

On Thu, Mar 2, 2017 at 10:03 AM, Peter Eisentraut <
peter(dot)eisentraut(at)2ndquadrant(dot)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