# create table foo (n int);
# insert into foo select generate_series(1, 100000);

import psycopg2
import threading
import time

keep_running = True

def vacuum_thread(dsn):
  conn = psycopg2.connect(dsn)
  conn.set_isolation_level(0)
  cursor = conn.cursor()
  while keep_running:
    cursor.execute("VACUUM")

def update_thread(dsn):
  conn = psycopg2.connect(dsn)
  cursor = conn.cursor()
  while keep_running:
    cursor.execute("UPDATE foo SET n = n + 1")
    conn.commit()

def check_thread(dsn):
  conn = psycopg2.connect(dsn)
  conn.set_isolation_level(0)
  cursor = conn.cursor()
  while keep_running:
    cursor.execute("SELECT pg_check_visible('foo'::regclass)")
    for row in cursor:
      print row
    conn.rollback()

if __name__ == "__main__":
  dsn = "dbname=postgres"
  t1 = threading.Thread(target = vacuum_thread, args = [dsn])
  t1.start()
  t2 = threading.Thread(target = update_thread, args = [dsn])
  t2.start()
  t3 = threading.Thread(target = check_thread, args = [dsn])
  t3.start()
  try:
    time.sleep(86400)
  except KeyboardInterrupt:
    keep_running = False
  t1.join()
  t2.join()
  t3.join()