PHP Data Caching: Structures, Index Design Principles, and Code Examples

Data Cache Structures

Memory Cache

Memory cache stores data in RAM for fast access, commonly using Memcache or Redis. Example using PHP Memcache extension:

<?php
$memcache = new Memcache;
$memcache->connect('127.0.0.1', 11211) or die ("Could not connect");
$key = "user_data_1";
$data = $memcache->get($key);
if($data === false){
    // fetch from DB
    $data = getUserDataFromDB(1);
    // store in cache for 1 hour
    $memcache->set($key, $data, 0, 3600);
}
// use $data
...?>

File Cache

File cache saves data to a file, often in JSON format. Example using PHP file functions:

<?php
$cacheFile = "user_data_1.json";

if (file_exists($cacheFile) && time() - filemtime($cacheFile) < 3600) {
    // read from cache file
    $data = json_decode(file_get_contents($cacheFile), true);
} else {
    // fetch from DB
    $data = getUserDataFromDB(1);
    // write to cache file
    file_put_contents($cacheFile, json_encode($data));
}
// use $data
...?>

Database Cache

Database cache stores data in a DB, e.g., MySQL Memory engine or Redis. Example using PDO with a cache table:

<?php
$pdo = new PDO('mysql:host=localhost;dbname=test;charset=utf8', 'username', 'password');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$cacheTable = "user_data_cache";

$stmt = $pdo->prepare("SELECT * FROM $cacheTable WHERE id = ?");
$stmt->execute([1]);
$row = $stmt->fetch(PDO::FETCH_ASSOC);
if ($row) {
    $data = json_decode($row['data'], true);
} else {
    $data = getUserDataFromDB(1);
    $stmt = $pdo->prepare("INSERT INTO $cacheTable(id, data) VALUES(?, ?)");
    $stmt->execute([1, json_encode($data)]);
}
// use $data
...?>

Index Design Principles for Data Cache

Good index design improves cache read efficiency. Principles include unique keys, appropriate expiration, hotspot data optimization, efficient cache updates, and hierarchical caching.

Unique Index

Ensure cache keys are unique, e.g., using user ID as key in Memcache.

Consider Cache Expiration

Set suitable expiration times to avoid stale data, such as checking file modification time for file cache.

Hotspot Data Optimization

Pre‑load frequently accessed data into cache, e.g., storing hot rows directly in a cache table.

Efficient Cache Updates

Keep cache and database consistent, using triggers or stored procedures for automatic updates.

Cache Hierarchy

Use nested cache keys for multi‑level data, like combining user ID and data type.

Conclusion

By selecting appropriate cache structures and applying index design principles, PHP applications can achieve better performance and responsiveness.