AW: - Mailing list pgsql-sql
Hi,
is the Python code running inside the PostgreSQL instance?
If not, the performance penalty might only get marginally better because it always involves to copy the data to the client and back again.
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Stefan Sonnenberg-Carstens
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Von: Mark Teper [mailto:mark.teper@gmail.com]
Gesendet: Donnerstag, 2. Mai 2019 19:51
An: pgsql-sql@lists.postgresql.org
Betreff:
Hi,
I'm trying to build some numerical processing algorithms on Postgres Array data types. Using PL/Python I can get access to the numpy libraries but the performance is not great. A guess is that there is a lot of overhead going from Postgres -> Python List -> Numpy and back again.
I'd like to test if that's the issue, and potentially fix by creating a C extension to convert directly from Postgres Array types to Numpy Array types. I _think_ I have the C side somewhat working, but I can't get Postgres to use the transform.
What I have:
---
CREATE FUNCTION arr_to_np(val internal) RETURNS internal LANGUAGE C AS 'MODULE_PATHNAME', 'arr_to_np';
CREATE FUNCTION np_to_arr(val internal) RETURNS real[] LANGUAGE C AS 'MODULE_PATHNAME', 'np_to_arr';
CREATE TRANSFORM FOR real[] LANGUAGE plpythonu (
FROM SQL WITH FUNCTION arr_to_np(internal),
TO SQL WITH FUNCTION np_to_arr(internal)
);
CREATE FUNCTION fn (a integer[]) RETURNS integer
TRANSFORM FOR TYPE real[]
AS $$ return a $$ LANGUAGE plpythonu;
----
The problem is this produces an error that transforms for type "real" doesn't work. It doesn't seem to allow for transforms on array's as opposed to underlying types. Is it possible to tell it to apply the transform to the array?
Thanks,
Mark