Hyperion Reactor The Middle Child of History

Drupal tries to cater to 80% of the market by taking most decisions for you. Generally this is a good idea. But if you fall in the remaining 20% then you need to get your hands dirty and start hacking around. Drupal by default stores all sessions in the database. This is a good idea if your site does not get a lot of load. But as your site starts growing, this will soon become a major bottleneck. Storing sessions in memcache works best in such situations. Not only is memcache easy to maintain, install and work with, but also provides in depth stats about itself.

Consistent hashing is a scheme that provides hash table functionality in a way that the addition or removal of one slot does not significantly change the mapping of keys to slots. In contrast, in most traditional hash tables, a change in the number of array slots causes nearly all keys to be remapped. By using consistent hashing, only K/n keys need to be remapped on average, where K is the number of keys, and n is the number of slots.

servers = ['memcache1', 'memcache2', 'memcache3', 'memcache4']
servers[ 'product-1'.hash % servers.size ]
 
servers[ 'product-1'.hash % servers.size ] => "memcache4"
servers[ 'product-2'.hash % servers.size ] => "memcache1"