MongoDB从节点支持读请求

因为mongo的原生特性，从节点默认只做故障切换功能，不提供读的请求。正常情况下在从节点读请求会显示：

---

wanya:SECONDARY> show dbs

2020-09-27T13:36:43.126+0800 E QUERY    [js] Error: listDatabases failed:{

"operationTime" : Timestamp(1601185003, 2),

"ok" : 0,

"errmsg" : "not master and slaveOk=false",

"code" : 13435,

"codeName" : "NotMasterNoSlaveOk",

"$clusterTime" : {

 "clusterTime" : Timestamp(1601185003, 2),

 "signature" : {

  "hash" : BinData(0,"8baIHeEIJCzjugfNfZljMcxLf1k="),

  "keyId" : NumberLong("6842713381699321872")

 }

}

} :

_getErrorWithCode@src/mongo/shell/utils.js:25:13

Mongo.prototype.getDBs@src/mongo/shell/mongo.js:139:1

shellHelper.show@src/mongo/shell/utils.js:882:13

shellHelper@src/mongo/shell/utils.js:766:15

@(shellhelp2):1:1

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not master and slaveOk=false 从这句话可以看出从节点目前的配置不支持读请求，可以通过

rs.slaveOk();来支持读。