Understanding Memory Usage in Django Webserver Workers

If you are coming from the PHP world, you might be used to thinking that when a request reaches the web server, everything is parsed and processed from scratch. In Python, however, the behavior is a little different.

A Python web server (for example, Gunicorn) starts one or more worker processes and then continuously accepts and processes requests as a running server application. In this article, I will explore how memory is managed in that environment.

Startup time vs. request execution

When you run a Django web server (either the development server or a Gunicorn-based deployment), there are two phases of execution: startup, when the server application is initialized, and the request/response cycle, when a request is received and processed to return a response.

During startup, wsgi.py and get_wsgi_application() are executed once per worker at boot time, Django settings are evaluated, applications listed in INSTALLED_APPS are imported and registered, ready() methods of app configs are called, and URL patterns are compiled.

During request execution, the middleware chain processes the request, the URL is resolved, the view is executed, context managers run within the view, the template is rendered, the middleware chain processes the response, and the response is returned.

The Django development server runs a single worker process but uses threads to handle concurrent requests. Gunicorn runs multiple worker processes (separate copies of the server application). A common rule of thumb for Gunicorn configuration is (2 × number_of_CPU_cores) + 1 workers.

Little demo of shared memory between requests

If you have mutable globals in your Django code, they will be shared within the same worker process, even across threads.

Here's a simple example for demonstration purposes (note that this is an antipattern and should never be used in production):

from django.http import JsonResponse
from django.utils.timezone import now

TIMESTAMPS = []

def show_timestamps(request):
    TIMESTAMPS.append(now())
    return JsonResponse({"timestamps": TIMESTAMPS})

The output would be (manually indented for readability):

{"timestamps": [
  "2026-06-08T19:48:42.044Z", 
  "2026-06-08T19:48:43.875Z", 
  "2026-06-08T19:48:44.776Z"
]}

If you serve this application with Gunicorn using multiple workers and open the view in several tabs, refreshing them a few times, you will see that the timestamp list keeps growing. However, because each request may be served by a different worker, the timestamps returned by each worker will differ.

How RAM is managed

1. Compilation/setup state is persistent

When Django starts and the application server is initialized, the following objects live in process memory for the lifetime of the worker process:

• django.apps.registry.Apps (the app registry with all models)
• URL resolvers (urlpatterns)
• Middleware instances (if instantiated at startup)
• Cached template engines
• Database connection configurations (not connections themselves)

This memory normally remains allocated until the worker process restarts.

2. Execution state lives per-request

Each request creates objects that are local to that request's call stack—views, forms, querysets, serializers, and so on. Once the response is sent:

• Python's garbage collector normally reclaims those objects.
• There is no explicit Django cleanup; Django relies on Python's normal memory management.
• Request-scoped objects are cleaned up only after they go out of scope and no references to them remain.

Common bugs to avoid

1. Mutable module-level state

A mutable object defined at the module level persists across all requests handled by that worker process and will accumulate data from every user.

❌ BAD:

_recent_users = []

def dashboard(request):
    # leaks across requests!
    _recent_users.append(request.user.id)
    return render(
        request, 
        "dashboard.html", 
        {"recent": _recent_users}
    )

✅ GOOD — state belongs in the DB, cache, or session:

def dashboard(request):
    recent_users = get_recent_users_from_db()
    return render(
        request, 
        "dashboard.html", 
        {"recent": recent_users}
    )

2. Storing per-request data on a shared instance

Middleware instances live for the lifetime of the worker process. Storing anything request-specific on self means it will be shared across every request handled by that worker.

❌ BAD:

class AuditMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
        # shared across all requests!
        self.current_user = None

    def __call__(self, request):
        # User A's data visible when User B's request runs
        self.current_user = request.user
        return self.get_response(request)

✅ GOOD — attach data to the request object, which is scoped to a single request:

class AuditMiddleware:
    def __init__(self, get_response):
        # only immutable config on self
        self.get_response = get_response

    def __call__(self, request):
        # scoped to this request's lifetime
        request.current_user = request.user
        return self.get_response(request)

3. Class-level cache shared across instances

A class attribute is shared across all instances of that class and therefore across all requests. The first user's data may be cached and returned to everyone else.

❌ BAD:

class ReportGenerator:
    # class attribute, shared across all instances and all requests!
    _cache = {}

    def get_data(self, user):
        if "data" not in self._cache:
            # first user's data cached for everyone
            self._cache["data"] = expensive_query(user)  
        return self._cache["data"]

✅ GOOD — use the cache framework with a user-scoped key:

from django.core.cache import cache

class ReportGenerator:
    def get_data(self, user):
        key = f"report:{user.id}"
        return cache.get_or_set(
            key, 
            lambda: expensive_query(user), 
            timeout=300,
        )

Mental model

Before writing module-level code, ask yourself:

"If 1000 different users hit this worker, and this variable exists for all of them, is that safe?"

Location	Lifetime	Safe for user data?
Local variable in a view/function	Single request	✅ Yes
request object attributes	Single request	✅ Yes
threading.local()	Single thread	✅ Yes
Database / cache with scoped keys	Persistent but keyed	✅ Yes
self on a middleware/class instance	Worker lifetime	⚠️ Only immutable config
Module-level mutable variable	Worker lifetime	❌ Never user data
Class-level mutable attribute	Worker lifetime	❌ Never user data

Rule of thumb: immutable configuration (numbers, booleans, strings, bytes, tuples, frozensets, and None) belongs at module level; anything that varies by request, user, or time belongs in the request cycle.

Conclusion

A Django worker process has two separate memory areas: a startup state that lives for the lifetime of the worker process (app registry, URL resolvers, middleware instances, template engines) and a request state that exists only while handling a request (views, querysets, forms) and is reclaimed by Python's garbage collector afterward.

The main rule is that immutable configuration can live at the module level, but anything that depends on the current user or request should stay inside the request cycle, such as local variables or the request object.

That's because module-level variables, class attributes, and middleware instance state are shared by all requests handled by the same worker, making them unsafe for user-specific data and a common cause of memory leaks and data exposure bugs.

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Cover Picture by Jon Tyson