Caching and You!

To maximise performance, SimplePie includes a caching system which can be used with a file-based cache, database cache or a Memcache-backed cache system.

File-based caching is the easiest way to set up caching for SimplePie. All you need is a server-writable directory (we usually call it cache/)!

For example, let's say your script is at /var/www/script.php. To use file-based caching, you first need to make a new directory at /var/www/cache. Make sure this directory can be written to by PHP. If you're using cache/, there's nothing else to set up, as SimplePie defaults to this directory.

If you want to store your cache somewhere else, say /var/www/somewhereelse, you'll need to tell SimplePie to do that. Don't worry, it's super easy!

$feed->set_cache_location('/var/www/somewhereelse');

If you use relative paths (i.e. they don't start with /, be aware that these are relative to where your script is, not where SimplePie is.

SimplePie also supports using MySQL as a database store for the cache.

Before you get started, you'll need to create the correct schema for SimplePie. In your copy of SimplePie, find the file called db.sql and run the commands under the MySQL section on your database.

Once you've done that, setting up SimplePie is easy as pie!

$feed->set_cache_location('mysql://username:password@hostname:port/database');

Replace those placeholders with your actual values, and you're good to go!

By default, the database tables are not prefixed. To set the prefix, add ?prefix=sp_ to your cache location (where sp_ is your desired prefix).

As of SimplePie 1.3, Memcache databases are supported right out of the box.

To use Memcache for SimplePie's cache, simply set your cache location with a memcache: prefix:

$feed->set_cache_location('memcache://hostname:port/?timeout=3600&prefix=sp_');

Replace the above placeholders as needed. The timeout value is how long you want the Memcache values to last for. We recommend setting this to the same as your value for $feed→set_cache_duration(), which defaults to 3600.

SimplePie also makes it absurdly easy to write your own cache handler. To start, take a look at the Memcache handler (''SimplePie_Cache_Memcache'') as it's one of the easiest to understand.

In a nutshell, here's what you need to do:

This interface is your gateway to writing your own caching system. Follow the hints in the PHPDoc comments to ensure that you implement these methods correctly.

Every caching system has options given by a URL-style location. Your cache handler needs to have a distinctive and unique (for your system) prefix, which looks like a URL scheme. For example, the Memcache handler uses memcache, which means Memcache locations always start with memcache://.

Next, you need to let SimplePie know about your handler. Simply call SimplePie_Cache::register() (pretending that we picked example as a prefix, and our handler class is ExampleCacheHandler)

SimplePie_Cache::register('example', 'ExampleCacheHandler');

Finally, tell SimplePie to use your cache handler. This is as easy as setting the cache location when you're using SimplePie.

$feed->set_cache_location('example://myhost/example');

• How does SimplePie's caching system work?
• I'm getting cache error messages