Question

I’m using Zend_Cache to cache data generated from a web service. However, in the event the web service does not respond, I want to display the outdated information and not leave a blank space.

According to the documentation, the answer is to pass the second argument to Zend_Cache_Core::load():

@param  boolean $doNotTestCacheValidity If set to true, the cache validity won't be tested

However, for every test I’ve done this always returns bool(false) for expired cache content.

Is there a way to force Zend_Cache to return the cached data for a given cache key, even when it has expired?

$cache_key = md5($url);
if ($out = $cache->load($cache_key)) {
  return $out;
}

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);

if ($output) {
  // Process...
  $cn_cache->save($out, $cache_key);
} else {
  // The query has timed out/web service not responded
  // We need to load the outdated cached content... but the following DOES NOT work
  return $cache->load($cache_key, true);

  // var_dump($cache->load($cache_key, true)); # false
}

Answer 1

I can’t think of a reliable way to do this other than to have a second cached version of the object that never expires. If you set a cache expiration time of X seconds on an object, there’s simply no way to guarantee that the object will still be there after X seconds.

Example proposed workaround below…

...
$cache_key_forever = sha1($url)
if ($output) {
  // Process...
  $cn_cache->save($out, $cache_key);
  $cn_cache->save($out, $cache_key_forever, array(), null); // The "null" parameter is the important one here: save cache indefinitely
} else {
  // The query has timed out/web service not responded
  // Load the infinitely persisted cache object
  return $cache->load($cache_key_forever);

  // var_dump($cache->load($cache_key, true)); # false
}