A, shard and replica mechanism
A, index comprising a plurality of shard
B, each shard is a minimum unit of work, carrying part of the data, Lucene instances, complete index and the ability to handle requests
C, de nodes increases or decreases, shard automatically load balancing node in
D, primary shard and replica shard, each document must exist only a certain primary shard and its corresponding replica shard in, can not exist in a plurality of primary shard
E, replica shard is the primary shard copy, responsible for fault tolerance and load bear a read request
F, the number of primary shard in the creation of the index is fixed, and the number of replica shard can be modified at any time
G, primary shard and its replica shard not on the same node, but may be other nodes on the same primary shard