Django persistent database connection

Question

I\'m using django with apache and mod_wsgi and PostgreSQL (all on same host), and I need to handle a lot of simple dynamic page requests (hundreds per second). I faced with

Answer 1

I made some small custom psycopg2 backend that implements persistent connection using global variable. With this I was able to improve the amout of requests per second from 350 to 1600 (on very simple page with few selects) Just save it in the file called base.py in any directory (e.g. postgresql_psycopg2_persistent) and set in settings

DATABASE_ENGINE to projectname.postgresql_psycopg2_persistent

NOTE!!! the code is not threadsafe - you can't use it with python threads because of unexpectable results, in case of mod_wsgi please use prefork daemon mode with threads=1

---

# Custom DB backend postgresql_psycopg2 based
# implements persistent database connection using global variable

from django.db.backends.postgresql_psycopg2.base import DatabaseError, DatabaseWrapper as BaseDatabaseWrapper, \
    IntegrityError
from psycopg2 import OperationalError

connection = None

class DatabaseWrapper(BaseDatabaseWrapper):
    def _cursor(self, *args, **kwargs):
        global connection
        if connection is not None and self.connection is None:
            try: # Check if connection is alive
                connection.cursor().execute('SELECT 1')
            except OperationalError: # The connection is not working, need reconnect
                connection = None
            else:
                self.connection = connection
        cursor = super(DatabaseWrapper, self)._cursor(*args, **kwargs)
        if connection is None and self.connection is not None:
            connection = self.connection
        return cursor

    def close(self):
        if self.connection is not None:
            self.connection.commit()
            self.connection = None

---

Or here is a thread safe one, but python threads don't use multiple cores, so you won't get such performance boost as with previous one. You can use this one with multi process one too.

# Custom DB backend postgresql_psycopg2 based
# implements persistent database connection using thread local storage
from threading import local

from django.db.backends.postgresql_psycopg2.base import DatabaseError, \
    DatabaseWrapper as BaseDatabaseWrapper, IntegrityError
from psycopg2 import OperationalError

threadlocal = local()

class DatabaseWrapper(BaseDatabaseWrapper):
    def _cursor(self, *args, **kwargs):
        if hasattr(threadlocal, 'connection') and threadlocal.connection is \
            not None and self.connection is None:
            try: # Check if connection is alive
                threadlocal.connection.cursor().execute('SELECT 1')
            except OperationalError: # The connection is not working, need reconnect
                threadlocal.connection = None
            else:
                self.connection = threadlocal.connection
        cursor = super(DatabaseWrapper, self)._cursor(*args, **kwargs)
        if (not hasattr(threadlocal, 'connection') or threadlocal.connection \
             is None) and self.connection is not None:
            threadlocal.connection = self.connection
        return cursor

    def close(self):
        if self.connection is not None:
            self.connection.commit()
            self.connection = None