Patterns for clearing Zend Cache

Question

I started using Zend Cache (APC backend) and all is well in terms of returning cached values instead of hitting the Database each time. However, heres my problem:

$cache_key = 'getrebates_'.$operator_code;

if(PP_Model_CacheService::exists($cache_key)) {
    $cached_values = PP_Model_CacheService::load($cache_key);
} else {
   //hits the db    
   $cached_values = $this->getAll($operator_code);
   PP_Model_CacheService::save($cached_values, $cache_key);
}
return $cached_values;

Each operator has their own rebates which vary between operators, now if I change the database and need to clear the rebates for all the operators, how would I do this?

I can use $Cache->clean(), but that will clear the other caches (not just the rebate cache for each operator). If I loop through all operators:

foreach($operator_codes AS $operator_code) {
   $cache_key = 'getrebates_'.$operator_code;
   $cache->delete($cache_key)
}

That seems like alot of work for the cache. Is there a way to clear just a section of Cache.

//Something like:
$section_key = 'getrebates';
$Cache[$section_key][$operator_code];
$Cache->clearSection($section_key);

Is there any array structure to the APC cache or is it all cache key/value based?

Symonds

Answer 1

You can apply tags to values stored in the cache. That way you can easily delete all cache entries which have a certain tag.

$cache->save($huge_data, 'myUniqueID', array('tagA', 'tagB'));

// clear all cache entries with tag tagA or tagC
$cache->clean(
  Zend_Cache::CLEANING_MODE_MATCHING_TAG,
  array('tagA', 'tagC')
);

Refer to this page: http://framework.zend.com/manual/en/zend.cache.theory.html and the API for details about the clean method of Zend_Cache_Core: http://framework.zend.com/apidoc/1.11/

Trona

Thanks for your time duke. As regilero pointed out below APC doesn't support tags. Which backend would you use in this case to support tags? – Symonds

How many cache entries are we talking about? If its 10 or 20 I would just delete each entry. Depending on your needs you could consider saving a serialized associative array into the cache instead of individual entries. This is not a good idea if you have to update/delete individual entries often though – Trona

Answer 2

@theduke is right, tagging is the right way to do it, except for APC, as Zend_Cache_Backend_Apc does not support tagging. From the doc:

Be careful : with this backend, "tags" are not supported for the moment

And from your last comment it sems you are using APC as a backend. So either you extend this class and add the Tag behavior (by adding a special syntax in tag identifier? by handling the tag vs cache entry mapping somewhere else?, in a long-term cache entry?), or you decide to use another cache backend.

Helper

Which backend supports tags? It seems like most of the backends don't from the Zend Manual – Symonds

from framework.zend.com/manual/en/zend.cache.backends.html you can see tags are available for file backend, SQLite backend and partially on ZendPlatform. – Helper