Redis Patterns (Pub/Sub, Sorted Sets, Lua)

Also Known As

TL;DR

Explanation

Redis data structures enable sophisticated patterns: Sorted Sets (ZADD/ZRANGE) for leaderboards and priority queues; Lists (LPUSH/BRPOP) for FIFO job queues; Sets for unique visitor counting; Hashes for session storage; INCR/EXPIRE for atomic rate limiting counters; Pub/Sub for real-time notifications; Lua scripts for atomic multi-step operations without round-trips; and SET key value NX EX for distributed locks (Redlock for multi-node). Redis Streams (XADD/XREAD) provide durable message queues with consumer groups, persistent delivery, and acknowledgement. PHP clients: Predis (pure PHP) and phpredis (C extension, faster).

Common Misconception

Why It Matters

Common Mistakes

• Using Redis as a primary database without persistence configured — data is lost on restart without RDB/AOF.
• Not setting TTLs on cached keys — Redis fills memory and starts evicting keys unpredictably.
• Using KEYS * in production — it blocks Redis while scanning all keys; use SCAN instead.
• Not using pipelines for multiple sequential Redis commands — each round trip adds latency.

Code Examples

// N sequential Redis calls — N round trips:
foreach ($userIds as $id) {
    $name = $redis->get("user:$id:name"); // 1 round trip per user
}

// Pipeline — 1 round trip for all:
$pipe = $redis->pipeline();
foreach ($userIds as $id) { $pipe->get("user:$id:name"); }
$names = $pipe->execute();

// String — simple cache
$redis->set('user:42:name', 'Alice', ['ex' => 300]);

// Hash — object storage without serialisation
$redis->hSet('user:42', 'name', 'Alice');
$redis->hSet('user:42', 'email', 'alice@example.com');
$name = $redis->hGet('user:42', 'name');

// Sorted set — leaderboard
$redis->zAdd('leaderboard', 1500, 'alice');
$top10 = $redis->zRevRange('leaderboard', 0, 9, true); // with scores

// List — simple queue
$redis->lPush('email_queue', json_encode($message));
$job = $redis->rPop('email_queue');

// Atomic counter — rate limiting
$redis->incr('api_hits:' . date('YmdH') . ':' . $ip);

References

• ↗ https://redis.io/docs/manual/patterns/

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