psycopg2/examples/threads.py

# threads.py -- example of multiple threads using psycopg
# -*- encoding: latin1 -*-
#
# Copyright (C) 2001-2010 Federico Di Gregorio  <fog@debian.org>
#
# psycopg2 is free software: you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# psycopg2 is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
# License for more details.

## put in DSN your DSN string

DSN = 'dbname=test'

## some others parameters
INSERT_THREADS = ('A', 'B', 'C')
SELECT_THREADS = ('1', '2')

ROWS = 1000

COMMIT_STEP = 20
SELECT_SIZE = 10000
SELECT_STEP = 500
SELECT_DIV  = 250

# the available modes are:
# 0 - one connection for all inserts and one for all select threads
# 1 - connections generated using the connection pool

MODE = 1

## don't modify anything below this line (except for experimenting)

import sys, psycopg2, threading
from psycopg2.pool import ThreadedConnectionPool
from psycopg2.extensions import ISOLATION_LEVEL_AUTOCOMMIT

if len(sys.argv) > 1:
    DSN = sys.argv[1]
if len(sys.argv) > 2:
    MODE = int(sys.argv[2])

print("Opening connection using dsn:", DSN)
conn = psycopg2.connect(DSN)
curs = conn.cursor()

try:
    curs.execute("""CREATE TABLE test_threads (
                        name text, value1 int4, value2 float)""")
except:
    conn.rollback()
    curs.execute("DROP TABLE test_threads")
    curs.execute("""CREATE TABLE test_threads (
                        name text, value1 int4, value2 float)""")
conn.commit()


## this function inserts a big number of rows and creates and destroys
## a large number of cursors

def insert_func(conn_or_pool, rows):
    name = threading.currentThread().getName()

    if MODE == 0:
        conn = conn_or_pool
    else:
        conn = conn_or_pool.getconn()

    for i in range(rows):
        if divmod(i, COMMIT_STEP)[1] == 0:
            conn.commit()
            if MODE == 1:
                conn_or_pool.putconn(conn)
            s = name + ": COMMIT STEP " + str(i)
            print(s)
            if MODE == 1:
                conn = conn_or_pool.getconn()
        c = conn.cursor()
        try:
            c.execute("INSERT INTO test_threads VALUES (%s, %s, %s)",
                      (str(i), i, float(i)))
        except psycopg2.ProgrammingError as err:
            print(name, ": an error occurred; skipping this insert")
            print(err)
    conn.commit()

## a nice select function that prints the current number of rows in the
## database (and transfer them, putting some pressure on the network)

def select_func(conn_or_pool, z):
    name = threading.currentThread().getName()

    if MODE == 0:
        conn = conn_or_pool
        conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)

    for i in range(SELECT_SIZE):
        if divmod(i, SELECT_STEP)[1] == 0:
            try:
                if MODE == 1:
                    conn = conn_or_pool.getconn()
                    conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)
                c = conn.cursor()
                c.execute("SELECT * FROM test_threads WHERE value2 < %s",
                          (int(i/z),))
                l = c.fetchall()
                if MODE == 1:
                    conn_or_pool.putconn(conn)
                s = name + ": number of rows fetched: " + str(len(l))
                print(s)
            except psycopg2.ProgrammingError as err:
                print(name, ": an error occurred; skipping this select")
                print(err)

## create the connection pool or the connections
if MODE == 0:
    conn_insert = psycopg2.connect(DSN)
    conn_select = psycopg2.connect(DSN)
else:
    m = len(INSERT_THREADS) + len(SELECT_THREADS)
    n = m/2
    conn_insert = conn_select = ThreadedConnectionPool(n, m, DSN)

## create the threads
threads = []

print("Creating INSERT threads:")
for name in INSERT_THREADS:
    t = threading.Thread(None, insert_func, 'Thread-'+name,
                         (conn_insert, ROWS))
    t.setDaemon(0)
    threads.append(t)

print("Creating SELECT threads:")
for name in SELECT_THREADS:
    t = threading.Thread(None, select_func, 'Thread-'+name,
                         (conn_select, SELECT_DIV))
    t.setDaemon(0)
    threads.append(t)

## really start the threads now
for t in threads:
    t.start()

# and wait for them to finish
for t in threads:
    t.join()
    print(t.getName(), "exited OK")


conn.commit()
curs.execute("SELECT count(name) FROM test_threads")
print("Inserted", curs.fetchone()[0], "rows.")

curs.execute("DROP TABLE test_threads")
conn.commit()