Deleting Redis Keys by Pattern in PHP (Detailed Guide w/ Code Examples)

Use Case(s)

Deleting Redis keys by a pattern is commonly used when you need to remove multiple keys that share a common naming scheme. Typical examples would be session keys prefixed by user id or cache keys with a common prefix.

Code Examples

Let's assume we have a Redis instance and connection established via Predis client:

$client = new Predis\Client();

Example 1: Delete keys matching a certain pattern:

$keys = $client->keys('pattern*');
foreach ($keys as $key) {
   $client->del($key);
}

In this example, we first get all keys matching the pattern 'pattern*' and then delete each key individually.

Example 2: If you want to delete keys across different databases (if your Redis setup has multiple databases), you need to select each database and perform the deletion operation:

for ($i = 0; $i < $numDatabases; $i++) {
   $client->select($i);
   $keys = $client->keys('pattern*');
   foreach ($keys as $key) {
      $client->del($key);
   }
}

Best Practices

1. Be very careful with the keys command in a production environment because it can potentially block the server while it's retrieving keys, especially when you have many keys.
2. Instead of using del, consider using unlink which is a non-blocking delete operation in Redis.

Common Mistakes

1. Not properly defining the key pattern which can lead to deletion of unintended keys.
2. Using keys command in production, it's better to use scan for large datasets to avoid blocking the server.

FAQs

Q: Can I delete keys by pattern in one command?

A: Redis does not provide an atomic operation to delete keys by pattern. You need to get all keys by pattern first using keys or scan, then delete them individually.