Memcached - Why data is not stored?

Question

I'm actually trying to understand why memcached is not storing data for a given Id.

I'm using Magento EE 1.11.2.0 that is based on Zend Framework 1.11.1.
The interface used to deal with Memcached is Zend_Cache_Backend_Memcached

Now there is not such big custom code here, this is my custom container that save the cache:

public function saveCache($blockContent)
{

    $lifeTime = 86400 * 30 * 6;
    $tags = array(
        My_Module_Model_PageCache_Container_Category_Blabla::CACHE_TAG
    );
    $cacheId = $this->_getCacheId();

    if ($cacheId !== false) {
        $this->_saveCache($blockContent, $cacheId, $tags, $lifeTime);
    }
    return $this;
}

I'm just forcing Magento to use my custom cache tag and a fixed lifetime ( Memcached doesn't support custom tag so I guess this is not the problem ) also my lifetime is not used in Memcached because I can see that the default one is used.

At the beginning I thought the issue was caused by a to long cache ID but now after reducing it ( <31 char ) this didn't help me:

I can see that the load() method Zend_Cache_Backend_Memcached return always false for my cache ids. While the save() method return true like if it was cached.

This is my local.xml configuration:

<cache>
        <slow_backend_store_data>1</slow_backend_store_data>
        <auto_refresh_fast_cache>0</auto_refresh_fast_cache>
        <backend>memcached</backend>
        <slow_backend>database</slow_backend>
        <memcached>
            <servers>
                <!--<server>-->
                <!--<host><![CDATA[127.0.0.1]]></host>-->
                <!--<port><![CDATA[11213]]></port>-->
                <!--<persistent><![CDATA[1]]></persistent>-->
                <!--</server>-->

                <server>
                    <host><![CDATA[unix:///tmp/memcached.sock]]></host>
                    <port><![CDATA[0]]></port>
                    <persistent><![CDATA[0]]></persistent>
                    <weight><![CDATA[2]]></weight>
                    <timeout><![CDATA[5]]></timeout>
                </server>
            </servers>
            <compression><![CDATA[0]]></compression>
            <hashed_directory_level><![CDATA[]]></hashed_directory_level>
            <hashed_directory_umask><![CDATA[]]></hashed_directory_umask>
            <file_name_prefix><![CDATA[]]></file_name_prefix>
        </memcached>
    </cache>
    <full_page_cache>
        <backend>memcached</backend>
        <slow_backend>database</slow_backend>
        <slow_backend_store_data><![CDATA[1]]></slow_backend_store_data>
        <memcached>
            <servers>
                <server>
                    <host><![CDATA[unix:///tmp/memcached.sock]]></host>
                    <port><![CDATA[0]]></port>
                    <persistent><![CDATA[0]]></persistent>
                    <weight><![CDATA[2]]></weight>
                    <timeout><![CDATA[10]]></timeout>
                    <retry_interval><![CDATA[10]]></retry_interval>
                    <status><![CDATA[1]]></status>
                    <stats_update_factor><![CDATA[1]]></stats_update_factor>
                </server>
            </servers>
        </memcached>
    </full_page_cache>

I also tried to check the entry of memcached to see if my id was stored or not with this command:

echo 'stats cachedump 35 35' | sudo nc -U /tmp/memcached.sock

• Any idea about the reason of this ?
• How can I debug it ? ( I cannot go under Zend_Cache_Backend_Memcached with xdebug)

There also a small things I don't understand:

• Even if I specify my <cache_lifetime> in my placeholder config that value is not used ? ( that is why I'm overriding the save() method )

Answer 1

here the issue is $lifetime and a relative bug in Zend_Cache_Backend_Memcached.

Memcached has a max lifetime of 30 days (2592000) so the limit I was using it was too big and that is why the data was not stored.

Sadly:

1. Zend_Cache_Backend_Memcached::save() doesn't check if the limit is correct < 2592000

2. the set() method on the memcached object return true even if it doesn't store the data $result = @$this->_memcache->set($id, array($data, time(), $lifetime), $flag, $lifetime);