Reference library

System design patterns

Sharding, load balancing, CAP tradeoffs, and scaling patterns — interview and production ready.

29 matches

Object Pool Pattern for Database Connections in Python

Implements a reusable connection pool with acquire/release and context manager support, mocking database connections with idle reuse and exhaustion handling.

object-pool connection-pool databases

Python

import time
from contextlib import contextmanager
from collections import deque


class ConnectionPool:
    def __init__(self, size=3, max_idle=5):
        self._idle = deque(maxlen=max_idle)
        self._active = set()
        self.size = size

    def _create(self):
        return {"created_at": time.time(), "queri…

12 0 Open

System design patterns medium

Outbox pattern reliable publish in Python with SQLite

Implements a transactional outbox with SQLite, ensuring reliable message publishing by storing events in the same DB transaction as business changes.

outbox sqlite transaction

Python

import sqlite3
from contextlib import contextmanager
from datetime import datetime, timezone


class Outbox:
    def __init__(self, db_path=":memory:"):
        self.conn = sqlite3.connect(db_path)
        self.conn.execute("""
            CREATE TABLE IF NOT EXISTS outbox (
                id INTEGER PRIMARY KEY AUTO…

11 0 Open

System design patterns medium

Simulate a Leaky Bucket Rate Limiter in Python

This code implements a leaky bucket rate limiter that drains at a fixed rate and accepts or rejects incoming requests based on capacity.

rate limiting leaky bucket simulation

Python

import time
from collections import deque


class LeakyBucket:
    """Simulates a leaky bucket rate limiter with a fixed drain rate."""
    def __init__(self, capacity, drain_rate_per_sec):
        self.capacity = capacity
        self.drain_rate = drain_rate_per_sec
        self.water = 0.0
        self.last_refill =…

13 0 Open

System design patterns medium

Singleton Config Loader in Python with Caution

Implements a singleton config loader in Python that reads JSON config files, but demonstrates the hidden gotcha of shared state across instances.

singleton config design-patterns

Python

import json
from pathlib import Path

class ConfigLoader:
    _instance = None

    def __new__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance

    def __init__(self, config_file="config.json"):
        if not hasattr(self, "loaded…

12 0 Open

System design patterns medium

Template Method Workflow Steps Base Class in Python

Define a reusable workflow skeleton in a base class and let subclasses fill in each step with the Template Method design pattern.

template-method design-patterns abc

Python

from abc import ABC, abstractmethod


class DataPipeline(ABC):
    """Template Method pattern: defines a workflow skeleton."""

    def run(self):
        """Template method - defines the algorithm's structure."""
        result = {"extracted": False, "transformed": False, "loaded": False}
        raw_data = self._ext…

13 0 Open

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