Replica Set Read and Write Semantics副本集读写语义
From the perspective of a client application, whether a MongoDB instance is running as a single server (i.e. "standalone") or a replica set is transparent. 从客户端应用程序的角度来看，MongoDB实例是作为单个服务器（即“独立”）还是副本集运行是透明的。However, MongoDB provides additional read and write configurations for replica sets.但是，MongoDB为副本集提供了额外的读写配置。
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Sharded clusters where the shards are also replica sets provide the same operational semantics with regards to write and read operations.分片也是副本集的分片集群提供了与写和读操作相同的操作语义。
Write Concern for Replica Sets副本集的写入关注Write concern describes the level of acknowledgement requested from MongoDB for write operations.写入关注描述了MongoDB为写操作请求的确认级别。Read Preference读取首选项Read preference specifies where (i.e. which members of the replica set) the drivers should direct the read operations.读取首选项指定驱动程序应将读取操作指向何处（即副本集的哪些成员）。Server Selection Algorithm服务器选择算法Describes the mechanics of read preference.描述阅读偏好的机制。