Caching & Redis
Cache-aside, TTL, invalidation, hot keys, and in-memory lookup patterns at scale.
Cache Stampede Prevention with SingleFlight in Python
Implements a SingleFlight pattern in Python to deduplicate concurrent cache-miss computations and prevent cache stampede.
import threading
import time
from functools import wraps
class SingleFlight:
def __init__(self):
self._lock = threading.Lock()
self._inflight = None
def do(self, key, fn):
with self._lock:
if self._inflight is not None:
return self._inflight[1]
…Coalescing duplicate in-flight requests: one shared result for concurrent callers
Runs identical concurrent requests through a single shared call, caching the result while it's in flight and returning the same value to all callers.
import time
import threading
from collections import defaultdict
class CoalescingExecutor:
def __init__(self):
self._locks = defaultdict(threading.Lock)
self._in_flight = {}
def execute(self, key, func):
with self._locks[key]:
if key in self._in_flight:
re…How to Implement a Write-Through Cache in Python with a Mock Database
A thread-safe write-through cache that updates both cache and mock database atomically, computing values only after a successful write to the database.
import threading
import time
import random
class WriteThroughCache:
def __init__(self):
self.cache = {}
self.db = {}
self.lock = threading.Lock()
def write(self, key, value):
with self.lock:
# Simulate slow database write
time.sleep(random.uniform(0.01…How to implement Redlock distributed lock in Python
Simulate Redis Redlock multi-instance locking to show how a distributed lock is acquired only when a majority of instances agree.
import time
import random
import threading
from dataclasses import dataclass
@dataclass
class MockRedisLock:
"""Simple mock of a Redis lock instance."""
name: str
key: str
ttl: int
acquired: bool = False
expires_at: float = 0.0
def acquire(self, sleep_fn=time.sleep):
"""Try to ac…Mock Redis Distributed Lock in Python with SET NX EX
A minimal in-memory mock of Redis SET NX EX distributed lock semantics for testing concurrent code without a real Redis server.
import time
import threading
import uuid
from typing import Optional
class RedisLockMock:
"""A minimal mock of Redis SET NX EX distributed lock semantics."""
def __init__(self):
self._store = {} # key -> (value, expiry_epoch)
def acquire(self, key: str, token: str, ttl_seconds: int) -> bool:
…Python Redis WATCH optimistic lock mock
A MockRedis class that simulates WATCH/MULTI/EXEC transactions with optimistic locking to detect concurrent modifications before committing.
import time
import threading
class MockRedis:
def __init__(self):
self.data = {}
self.watched = {}
self.lock = threading.Lock()
def get(self, key):
return self.data.get(key)
def set(self, key, value):
self.data[key] = value
def watch(self, *keys):
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Caching & Redis — Python code examples
What you will find here
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