mongo查询抛出异常，什么原因

mongo查询抛出异常，什么原因

OperationFailure: could not find host matching read preference { mode: "primary", tags: [ {} ] } for set rs1

请确认下rs1这个副本集当前的primary是否正常

primary All read operations use only the current replica set primary. [5] This is the default read mode. If the primary is unavailable, read operations produce an error or throw an exception. 看样子的确是这样. primary 服务器不可用。