Golang MGO driver specifies MONGO server read

This is a creation in Article, where the information may have evolved or changed.

Replica Sets Construction

The server is built with Replica sets and can be referenced by deploy a Replica Set

Read mode

There are five types of reading modes in Mongod:

• Primary. Perform all read operations on the master node
• Primarypreferred. Read operations are preferred on the primary node, if the primary node is unavailable and then from the node.
• Secondary. All read operations are performed on the slave node.
• Secondarypreferred. Priority is read from the node, if all slave nodes are not available, then operate from the master node.
• Nearest. Depending on the network latency, read operations are performed nearby, regardless of the node type.

Configuration Node Tags sets

Tag sets allows you to specify a replica set for read operations where the read mode of Mongod must be one of the following four types:
primaryPreferred, secondary , secondaryPreferred ,nearest
Tags Sets Configuration reference: Configure Replica Set Tag Sets
The main operations are as follows:

conf = rs.conf()conf.members[0].tags = { "dc": "east", "use": "production"  }conf.members[1].tags = { "dc": "east", "use": "reporting"  }conf.members[2].tags = { "use": "production"  }rs.reconfig(conf)

MgO code Example

Depending on the configuration above, if you need to specify a database read from members 1, you can take the following code:

session, err := mgo.Dial("localhost")if err != nil {    log.Fatalln(err)}defer session.Close()session.SetMode(mgo.Eventual, true) //需要指定为Eventualsession.SelectServers(bson.D{{"dc", "east"}, {"use", "reporting"}}) // 指定从1中读取db := session.DB("test")col := db.C("tbl")data := make([]interface{}, 10)col.Find(nil).Limit(10).All(&data)log.Println(data)