Redis as message broker in Flask - Performance & Optimization

Performance: Redis as message broker

MEDIUM IMPACT

This affects the responsiveness and throughput of message passing between components in a web application.

Passing messages between Flask app components asynchronously

Flask

import redis
from flask import Flask
app = Flask(__name__)
r = redis.Redis()

@app.route('/send/<msg>')
def send(msg):
    r.lpush('messages', msg)
    return 'Message sent'

@app.route('/receive')
def receive():
    msg = r.rpop('messages')
    return msg.decode() if msg else 'No messages'

Offloads message storage and retrieval to Redis, enabling non-blocking, fast message passing.

📈 Performance GainNon-blocking IO; reduces main thread load; supports high concurrency

Passing messages between Flask app components asynchronously

Flask

from flask import Flask
app = Flask(__name__)

messages = []

@app.route('/send/<msg>')
def send(msg):
    messages.append(msg)
    return 'Message sent'

@app.route('/receive')
def receive():
    if messages:
        return messages.pop(0)
    return 'No messages'

Storing messages in a list in memory blocks the main thread and does not scale well under load.

📉 Performance CostBlocks rendering for each message; causes slow response under concurrent requests

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
In-memory message queue in Flask	None	Blocks main thread	Delays response rendering	[X] Bad
Redis message broker with Flask	None	Non-blocking	Fast response rendering	[OK] Good

Rendering Pipeline

Using Redis as a message broker moves message handling outside the Flask app process, reducing blocking during request handling.

→Interaction Handling

→Network IO

→JavaScript Event Loop

⚠️ BottleneckInteraction Handling when using in-memory message queues

Core Web Vital Affected

INP

This affects the responsiveness and throughput of message passing between components in a web application.

Optimization Tips

1Use Redis to handle message queues outside the Flask main thread.

2Avoid in-memory message queues that block request handling.

3Monitor interaction responsiveness (INP) when implementing message brokers.

Performance Quiz - 3 Questions

What is a key performance benefit of using Redis as a message broker in a Flask app?

A It increases the size of the Flask app bundle.

B It offloads message handling from the main thread, reducing blocking.

C It causes more DOM reflows during message passing.

D It delays the first contentful paint.

DevTools: Performance

How to check: Record a session sending and receiving messages; observe main thread activity and request durations.

What to look for: Look for reduced main thread blocking and faster request completion times with Redis.