Memcached::casByKey(PECL memcached >= 0.1.0) Memcached::casByKey — Compare and swap an item on a specific server Описание
   public bool Memcached::casByKey
    ( float $cas_token
   , string $server_key
   , string $key
   , mixed $value
   [, int $expiration
  ] ) 
  Memcached::casByKey() is functionally equivalent to Memcached::cas(), except that the free-form server_key can be used to map the key to a specific server. This is useful if you need to keep a bunch of related keys on a certain server. Список параметров
 
 Возвращаемые значенияВозвращает TRUE в случае успешного завершения или FALSE в случае возникновения ошибки. The Memcached::getResultCode() will return Memcached::RES_DATA_EXISTS if the item you are trying to store has been modified since you last fetched it.  | 
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