redis
rickatech 2016-09 (edit)

As of 2016 Redis has become the defacto memory cache for supporting all manner of web services, essentially replacing venerable memcache.

# yum install redis

# yum install php-pecl-redis

# systemctl status redis   

Most web servers default to storing web session state directly on local file system.  Redis can be used to store sessions in memory instead.  PHP is a popular service session framework, and it can be configured to detext and use redis service instead of local file store for sessions state.

# yum install redis

# yum install  php56w-pecl-redis

# diff /etc/httpd/conf.d/php.conf

23,25c23,28
< php_value session.save_handler "files"
< php_value session.save_path    "/var/lib/php/session"
< php_value soap.wsdl_cache_dir  "/var/lib/php/wsdlcache"
---
> php_value session.save_handler "redis"
> php_value session.save_path    "tcp://127.0.0.1:6379"
> php_value soap.wsdl_cache_dir  "tcp://127.0.0.1:6379"

# systemctl restart redis

# systemctl restart httpd 

$ cat .../session.php 

  <?php  //simple session counter for testing
  session_start();
  $count = isset($_SESSION['count']) ? $_SESSION['count'] : 1;
  echo $count;
  $_SESSION['count'] = ++$count;

$ redis-cli -h localhost

  > keys *

    1) "PHPREDIS_SESSION:fepl2i5rm53gn58qq8ii7tbi07"