Use Redis for Drupal sessions
a quick google search: http://lmgtfy.com/?q=drupal+redis+sessions

and the 2nd result talks about redis session handling:
https://www.drupal.org/node/2250195

from that issue thread i recommend looking Session Proxy. This allows you to override the default session handler by Drupal -- which is explained in the above issue:


  This is because Drupal will override your session handler and use its
  own, it goes straight to the database. I'd recomend that you try using
  this module: https://drupal.org/project/session_proxy


Session Proxy provides the following, I believe your attempting #2:


  ships three different session managing implementations:
  
  
  Database session handling: core default, ported to the object oriented
  API. It comes with an additional SQL query done more than core
  session.inc default implementation due to the API strong
  encapsulation.
  Native PHP session handling: by selecting this session
  management mode, you explicitely remove any core session management,
  and let PHP manage it. This can be useful if you intend to use
  low-level PHP extensions, such as Memcache or PhpRedis to handle
  session in PHP low-level layer instead of core. This allow to use any
  PHP native session storage to work gracefully: some of them are high
  performance.
  Cache based storage engine: Using the same session
  handling than core, but deporting raw session storage into a cache
  backend instance. You can use any already-functionning cache backend
  to store sessions. Sessions will use their own bin, and won't be
  cleared at cache clear all time.
  


Again from the linked issue after installing session proxy you likely need to configure your php.ini to something like:

session.save_handler = redis
session.save_path = "tcp://localhost:6379"