How to use python to query database in parallel

Question

I have two functions which I use to query database. Assuming two separate queries, how to run these in parallel to query same database, and also wait for both results to return before continuing the execution of the rest of the code?

def query1(param1, param2):
    result = None
    logging.info("Connecting to database...")
    try:
        conn = connect(host=host, port=port, database=db)
        curs = conn.cursor()
        curs.execute(query)
        result = curs
        curs.close()
        conn.close()
    except Exception as e:
        logging.error("Unable to access database %s" % str(e))
    return result


def query2(param1, param2):
    result = None 
    logging.info("Connecting to database...")
    try:
        conn = connect(host=host, port=port, database=db)
        curs = conn.cursor()
        curs.execute(query)
        result = curs
        curs.close()
        conn.close()  
    except Exception as e:
        logging.error("Unable to access database %s" % str(e))    
    return result

Answer 1

Here is a multi-threaded code that does what you're trying to accomplish:

from threading import Thread, Lock

class DatabaseWorker(Thread):
    __lock = Lock()

    def __init__(self, db, query, result_queue):
        Thread.__init__(self)
        self.db = db
        self.query = query
        self.result_queue = result_queue

    def run(self):
        result = None
        logging.info("Connecting to database...")
        try:
            conn = connect(host=host, port=port, database=self.db)
            curs = conn.cursor()
            curs.execute(self.query)
            result = curs
            curs.close()
            conn.close()
        except Exception as e:
            logging.error("Unable to access database %s" % str(e))
        self.result_queue.append(result)

delay = 1
result_queue = []
worker1 = DatabaseWorker("db1", "select something from sometable",
        result_queue)
worker2 = DatabaseWorker("db1", "select something from othertable",
        result_queue)
worker1.start()
worker2.start()

# Wait for the job to be done
while len(result_queue) < 2:
    sleep(delay)
job_done = True
worker1.join()
worker2.join()