Pl/Python runtime overhead

On Wed, Aug 7, 2013 at 7:43 AM, Seref Arikan
<serefarikan@kurumsalteknoloji.com> wrote:

When a pl/python based function is invoked, does it keep a python runtime
running across calls to same function? That is, if I use connection pooling,
can I save on the python runtime initialization and loading costs?

You can use the following wrapping technique to cache function's body,
that will save you some resources and time. It stores the main() in SD
(session data) built-in object and retrieves it when stored, so
plpython does not need to process it every time stored function is
called.

CREATE OR REPLACE FUNCTION some_plpython_function()
RETURNS integer
LANGUAGE plpythonu
AS $function$
""" An example of a function's body caching and error handling """

sdNamespace = 'some_plpython_function'

if sdNamespace not in SD:

def main():
""" The function is assumed to be cached in SD and reused """

result = None

# Do whatever you need here

return result

# Cache body in SD
SD[sdNamespace] = main

try:
return SD[sdNamespace]()
except Exception, e:
import traceback
plpy.info(traceback.format_exc())

$function$;

I can also recommend you to cache query plans, as plpython does not do
it itself. The code below also works with SD to store prepared plans
and retrieve them. This allows you to avoid preparing every time you
are executing the same query. Just like plpgsql does, but manually.

if SD.has_key('%s_somePlan' % sdNamespace):
somePlan = SD['%s_planName' % sdNamespace]
else:
somePlan = plpy.prepare(...)

Are there any documents/books etc you'd recommend to get a good
understanding of extending postgres with languages like python? I'd really
like to get a good grip of the architecture of this type of extension, and
possibly attempt to introduce a language of my own choosing. The docs I've
seen so far are mostly too specific, making it a bit for hard for me to see
the forest from the trees.

AFAIK, this one is the best one
http://www.postgresql.org/docs/9.2/interactive/plpython.html.

--
Kind regards,
Sergey Konoplev
PostgreSQL Consultant and DBA

http://www.linkedin.com/in/grayhemp
+1 (415) 867-9984, +7 (901) 903-0499, +7 (988) 888-1979
gray.ru@gmail.com

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Thanks Sergey,
This is going to help for sure. I'll also look at the url. What I've been
trying to understand is when python runtime is invoked during the function
execution (lifecycle?) . Maybe looking at plpython's source may help get an
understanding of that.

Regards
Seref

On Thu, Aug 8, 2013 at 2:54 AM, Sergey Konoplev <gray.ru@gmail.com> wrote:

On 8/7/13 10:43 AM, Seref Arikan wrote:

When a pl/python based function is invoked, does it keep a python
runtime running across calls to same function? That is, if I use
connection pooling, can I save on the python runtime initialization and
loading costs?

The Python interpreter is initialized once during a session, normally
when the first PL/Python function is called. So yes, connection pooling
can be helpful here.

Are there any documents/books etc you'd recommend to get a good
understanding of extending postgres with languages like python? I'd
really like to get a good grip of the architecture of this type of
extension, and possibly attempt to introduce a language of my own
choosing. The docs I've seen so far are mostly too specific, making it a
bit for hard for me to see the forest from the trees.

The basic documentation is here:
http://www.postgresql.org/docs/devel/static/plhandler.html. The rest is
mainly experience and copying from existing language handler
implementations.

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Thanks for the confirmation Peter,
I guess I'll take a good look at the existing implementations.

All the best
Seref

On Fri, Aug 9, 2013 at 10:24 PM, Peter Eisentraut <peter_e@gmx.net> wrote: