Caching Expensive Computations with Redis

Redis caches costly results with a time-to-live to reduce repeated computation.

The examples focus on the operation itself, including the important distinction: A per-request PHP array cache does not persist between requests.

What It Does

Use the examples below to observe the behavior on a small dataset before extending it to application code.

Before You Start

Read the input requirements before applying this pattern to production data.

Example 1: Basic Use

Cache expensive data with a bounded TTL; Redis is an optional PECL extension and requires a reachable server.

<?php
$cache = new Redis();
$cache->connect(getenv("REDIS_HOST") ?: "127.0.0.1", 6379);
$key = "report:3";
$hit = $cache->get($key);
if ($hit === false) {
    $hit = json_encode(["generatedAt" => gmdate("c")], JSON_THROW_ON_ERROR);
    $cache->setex($key, 120, $hit);
}
echo $hit;

This example is meant for a configured application environment; output depends on the installed extension, external service, or database contents.

Example 2: Checking Behavior

Cache expensive data with a bounded TTL; Redis is an optional PECL extension and requires a reachable server.

<?php
$cache = new Redis();
$cache->connect(getenv("REDIS_HOST") ?: "127.0.0.1", 6379);
$key = "report:8";
$hit = $cache->get($key);
if ($hit === false) {
    $hit = json_encode(["generatedAt" => gmdate("c")], JSON_THROW_ON_ERROR);
    $cache->setex($key, 120, $hit);
}
echo $hit;

This example is meant for a configured application environment; output depends on the installed extension, external service, or database contents.

Example 3: Practical Example

Cache expensive data with a bounded TTL; Redis is an optional PECL extension and requires a reachable server.

<?php
$cache = new Redis();
$cache->connect(getenv("REDIS_HOST") ?: "127.0.0.1", 6379);
$key = "report:21";
$hit = $cache->get($key);
if ($hit === false) {
    $hit = json_encode(["generatedAt" => gmdate("c")], JSON_THROW_ON_ERROR);
    $cache->setex($key, 120, $hit);
}
echo $hit;

This example is meant for a configured application environment; output depends on the installed extension, external service, or database contents.

Important Behavior and Edge Cases

Cache keys must include all parameters that change the result; Redis outages must not break the core operation.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• Redis caches costly results with a time-to-live to reduce repeated computation.
• Cache keys must include all parameters that change the result; Redis outages must not break the core operation.
• A per-request PHP array cache does not persist between requests.

Use Caching Expensive Computations with Redis when its documented behavior matches the problem. Test the relevant edge cases in your own runtime before deploying it.