join the nosql movement in all cases take popular festival such as tomorrowland festivals tend to have maximum allowed capacity for safety reasons if you sell more tickets than you're allowed because your servers kept on selling during node communication failureyou could sell double the number allowed by the time communications are reestablished in such case it might be wiser to go for consistency and turn off the nodes temporarily festival such as tomorrowland is sold out in the first couple of hours anywayso little downtime won' hurt as much as having to withdraw thousands of entry tickets the base principles of nosql databases rdbms follows the acid principlesnosql databases that don' follow acidsuch as the document stores and key-value storesfollow base base is set of much softer database promisesbasically available--availability is guaranteed in the cap sense taking the web shop exampleif node is up and runningyou can keep on shopping depending on how things are set upnodes can take over from other nodes elasticsearchfor exampleis nosql document-type search engine that divides and replicates its data in such way that node failure doesn' necessarily mean service failurevia the process of sharding each shard can be seen as an individual database server instancebut is also capable of communicating with the other shards to divide the workload as efficiently as possible (figure several shards can be present on single node if each shard has replica on another nodenode failure is easily remedied by re-dividing the work among the remaining nodes soft state--the state of system might change over time this corresponds to the eventual consistency principlethe system might have to change to make the data replica of shard shard replica of shard shard node replica of shard shard replica of shard shard node figure shardingeach shard can function as self-sufficient databasebut they also work together as whole the example represents two nodeseach containing four shardstwo main shards and two replicas failure of one node is backed up by the other