MDL-57655 session: Adds igbinary serializer to Redis session handler

config-dist.php

@@ -261,6 +261,9 @@ $CFG->admin = 'admin';
 //      $CFG->session_redis_prefix = ''; // Optional, default is don't set one.
 //      $CFG->session_redis_acquire_lock_timeout = 120;
 //      $CFG->session_redis_lock_expire = 7200;
+//      Use the igbinary serializer instead of the php default one. Note that phpredis must be compiled with
+//      igbinary support to make the setting to work. Also, if you change the serializer you have to flush the database!
+//      $CFG->session_redis_serializer_use_igbinary = false; // Optional, default is PHP builtin serializer.
 //
 //   Memcache session handler (requires memcached server and memcache extension):
 //      $CFG->session_handler_class = '\core\session\memcache';

lib/classes/session/redis.php

@@ -50,6 +50,8 @@ class redis extends handler {
     protected $prefix = '';
     /** @var int $acquiretimeout how long to wait for session lock in seconds */
     protected $acquiretimeout = 120;
+    /** @var int $serializer The serializer to use */
+    protected $serializer = \Redis::SERIALIZER_PHP;
     /**
      * @var int $lockexpire how long to wait in seconds before expiring the lock automatically
      * so that other requests may continue execution, ignored if PECL redis is below version 2.2.0.
@@ -91,6 +93,10 @@ class redis extends handler {
             $this->acquiretimeout = (int)$CFG->session_redis_acquire_lock_timeout;
         }
 
+        if (!empty($CFG->session_redis_serializer_use_igbinary) && defined('\Redis::SERIALIZER_IGBINARY')) {
+            $this->serializer = \Redis::SERIALIZER_IGBINARY; // Set igbinary serializer if phpredis supports it.
+        }
+
         // The following configures the session lifetime in redis to allow some
         // wriggle room in the user noticing they've been booted off and
         // letting them log back in before they lose their session entirely.
@@ -150,7 +156,7 @@ class redis extends handler {
             if (!$this->connection->connect($this->host, $this->port, 1)) {
                 throw new RedisException('Unable to connect to host.');
             }
-            if (!$this->connection->setOption(\Redis::OPT_SERIALIZER, \Redis::SERIALIZER_PHP)) {
+            if (!$this->connection->setOption(\Redis::OPT_SERIALIZER, $this->serializer)) {
                 throw new RedisException('Unable to set Redis PHP Serializer option.');
             }
 
@@ -389,4 +395,4 @@ class redis extends handler {
 
         $this->handler_destroy($sid);
     }
-}
\ No newline at end of file
+}