PHP Redis: Getting the Last Update Time (Detailed Guide w/ Code Examples)

Use Case(s)

Redis doesn't directly provide a method to get the last update time for a particular key. However, using PHP and Redis together, you can design a workaround by either setting an additional timestamp key whenever a key is updated or using the OBJECT IDLETIME command.

Code Examples

Here's an example of setting an additional key to track the update time:

<?php
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
$key = 'mykey';
$timestampKey = $key . ':timestamp';

// Setting value for mykey
$redis->set($key, 'Hello World!');

// Setting timestamp for mykey
$redis->set($timestampKey, time());

// Getting last update time for mykey
$lastUpdateTime = $redis->get($timestampKey);
echo 'Last update time: ' . date('Y-m-d H:i:s', $lastUpdateTime);
?>

In this example, we maintain a separate key (mykey:timestamp) to store the last update time each time mykey is updated.

Alternatively, you could use the OBJECT IDLETIME command, which returns the number of seconds since the last access (read or write) of the specified key. It's not exactly the last update time, but close enough for many use cases:

<?php
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);
$key = 'mykey';

$redis->set($key, 'Hello World!');

// Getting idle time for mykey
$idleTime = $redis->rawCommand('OBJECT', 'IDLETIME', $key);
echo 'Idle time in seconds: ' . $idleTime;
?>

Best Practices

• For high frequency updates, it may be more efficient to use the OBJECT IDLETIME method since maintaining a separate timestamp key for each primary key can increase storage requirements and slow down operations.

• When using OBJECT IDLETIME, remember that the idle time increases with each second the key is not accessed. So if you need the exact time of last update, this method may not work well for you.

Common Mistakes

• Forgetting to update the timestamp key when the primary key is updated.

• Not considering the extra storage that will be required for storing timestamp keys.

• Misunderstanding the OBJECT IDLETIME. It doesn't give the last update time but rather the time elapsed since the last access.

FAQs

Q: Can I directly get the last update time with Redis? A: No. Redis does not provide direct support for retrieving the last update time for a specific key. You can either maintain a separate timestamp key or use the OBJECT IDLETIME command as a workaround.

Q: Is there any performance impact by maintaining a separate timestamp key for each primary key? A: Yes, there could be. Each additional key requires additional storage and causes a slight overhead for every write operation.