How to test postgres statement_timeout in django

Question

I have added both connect and statement timeouts for a postgres database in my django service. So the relevant django setting looks like;

_CONN_TIMEOUT = 5
_STATEMENT_TIMEOUT = 3000 # millisecond
DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "some_database",
        # ...,
        "OPTIONS": {
            "connect_timeout": _CONN_TIMEOUT,
            "options": "-c statement_timeout={0}ms".format(_STATEMENT_TIMEOUT),
        },
    }
}

And then, I'm writing tests like this;

class DbTimeoutTest(TestCase):
    def test_db_statement_timeout(self):
        """
        test carrying out an SQL query that takes longer than the configured
        postgres `statement_timeout` value
        """
        # set statement_timeout to 1 millisecond
        mock_s_timeout = 1
        with self.settings(_CONN_TIMEOUT=5, _STATEMENT_TIMEOUT=mock_s_timeout):
            self.assertEqual(
                settings.DATABASES["default"]["OPTIONS"]["options"],
                "-c statement_timeout={0}ms".format(mock_s_timeout),
            )
            Book.objects.create(name="Hello")

However, that test is not working.

• The assert self.assertEqual does not pass, meaning that the setting override did not work.
• I would expect the Book.objects.create statement to fail with timeout but it does not.

So questions;

1. How do I test for postgres statement_timeout?(been able to also test for connect timeout would also be a plus)
2. How do I catch, the statement timeout error in my code?

Answer 1

Have a look the at django project's test case

They set the timeout to 1ms and assertRaises(OperationalError)

Full code:

def test_statement_timeout(self):
    databases = copy.deepcopy(settings.DATABASES)
    # Set timeout to 1ms and execute a 1s query.
    databases[DEFAULT_DB_ALIAS]['STATEMENT_TIMEOUT'] = 1
    new_connections = ConnectionHandler(databases)
    new_connection = new_connections[DEFAULT_DB_ALIAS]
    try:
        with new_connection.cursor() as cursor:
            with self.assertRaises(OperationalError):
                cursor.execute("SELECT pg_sleep(1)")
    finally:
        new_connection.close()

Answer 2

This is what I ended up doing;

In your settings.py file:

CONNECTION_TIMEOUT = 5 # seconds
STATEMENT_TIMEOUT = 3000 # milliseconds
DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "some_database",
        # ...,
        "OPTIONS": {
            "connect_timeout": CONNECTION_TIMEOUT,
            "options": "-c statement_timeout={0}ms".format(STATEMENT_TIMEOUT),
        },
    }
}

And in your test_database.py file:

from django.conf import settings
from django.test import TestCase
from django.db import connection
from django.db.utils import OperationalError


class DatabaseTest(TestCase):
    def test_timeout(self):
        statement_timeout_seconds = settings.STATEMENT_TIMEOUT / 1000
        cursor = connection.cursor()
        with self.assertRaises(OperationalError) as raised_exception:
            cursor.execute(
                # sql query that takes 3 times longer than the configured statement_timeout
                "SELECT pg_sleep({0})".format((statement_timeout_seconds) * 3)
            )
            cursor.fetchall()
        cursor.close()

        self.assertIn(
            "canceling statement due to statement timeout", str(raised_exception.exception)
        )