This command returns always FALSE when binary protocol in use (Memcached::OPT_BINARY_PROTOCOL = true). Without binary protocol it works.
(PECL memcached >= 2.0.0)
Memcached::getAllKeys — Gets the keys stored on all the servers
Memcached::getAllKeys() queries each memcache server and retrieves an array of all keys stored on them at that point in time. This is not an atomic operation, so it isn't a truly consistent snapshot of the keys at point in time. As memcache doesn't guarantee to return all keys you also cannot assume that all keys have been returned.
This function has no parameters.
Returns the keys stored on all the servers on success or
FALSE on failure.