Release question with psycopg2.ThreadConnectionPool, uWSGI and Flask

I am using Flask, psycopg2 and uWSGI. I am using psycopg2.ThreadConnectionPool

to join DB pools, and only cursor.callproc

used to query DB.

Problem: Sometimes during concurrent requests, the results of a procedure call are mixed, the code requests procedure_1

but gets the results for procedure_2

(and vice versa for another concurrent client). Even if in uwsgi.ini

there threads=1

, and only processes

used for concurrency. maxconn

for is psycopg2.ThreadConnectionPool

set to 1

. The problem goes away if the parameter is processes

set 1

touwsgi.ini

What could be causing the problem?

Here's a simplified code that reproduces the problem:

Flask app:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import contextlib

import flask
import psycopg2
import psycopg2.pool


app = flask.Flask(__name__)


class ThreadConnectionPool(psycopg2.pool.ThreadedConnectionPool):

    @contextlib.contextmanager
    def item(self):
    close = True
    connection = self.getconn()
    connection.autocommit = True
    try:
        yield connection
        close = False
    finally:
        self.putconn(connection, close=close or connection.closed)


pool = ThreadConnectionPool(maxconn=1, minconn=1, **kwargs)  # kwargs are omitted here 

# sp_1 always returns 1, sp_2 always returns 2
EXPECTED = {'sp_1': 1, 'sp_2': 2}


@app.route('/main/', methods=['GET'])
def main_handler():
    procname = flask.request.args['procname']

    with pool.item() as connection:
        cursor = connection.cursor()
        cursor.callproc(procname)

        rows = cursor.fetchall()

        if rows[0][0] == EXPECTED[procname]:
            return 'OK\n'
        else:
            # procedure returned something that it shouldn't return
            return 'ERROR\n'


if __name__ == '__main__':
    app.run()

      

        
        
        
      

    

uwsgi.ini:

[uwsgi]
callable=app
chdir=/path/to/my/project/
module=mymodule
master=True
processes=4 ; if 1, there is no problem
socket=127.0.0.1:9000
threads=1

      

        
        
        
      

    

Procedures:

-- sp_1
BEGIN
    Return 1;
END;


-- sp_2
BEGIN
    Return 2;
END;

      

        
        
        
      

    

Playback (this does not happen on every request, but rather often):

curl 'http://mymodule.local/main/?procname=sp_1' & curl 'http://mymodule.local/main/?procname=sp_2'
[1] 10636
ERROR
ERROR
[1]+  Done                    curl 'http://mymodule.local/main/?procname=sp_1'

      

        
        
        
      

    

Thanks in advance!