获取

### 获取一个文档 A document can be retrieved from a primary shard or from any of its replicas. [[img-distrib-read]].Retrieving a single documentimage::images/04-03_get.png["Retrieving a single document"] Below we list the sequence of steps to retrieve a document from either aprimary or replica shard, as depicted in <>: 1. The client sends a get request to `Node 1`. 1. The node uses the document's `_id` to determine that the documentbelongs to shard `0`. Copies of shard `0` exist on all three nodes.On this occasion, it forwards the request to `Node 2`. 1. `Node 2` returns the document to `Node 1` which returns the documentto the client. For read requests, the requesting node will choose a different shard copy onevery request in order to balance the load -- it round-robins through allshard copies. It is possible that a document has been indexed on the primary shard buthas not yet been copied to the replica shards. In this case a replicamight report that the document doesn't exist, while the primary would havereturned the document successfully.