通过nodejs驱动程序使用`secondary`作为读取首选项挂起查询命令？

Question

我正在使用mongodb3.6和nodejs mongo驱动程序3.0。以下是我的源代码：

const col = client.db('test').collection('test');
  col
    .insert({a: false}, {w: 0, j: false})
    .then(() => {
      return col.count({}, {readPreference: ReadPreference.SECONDARY});
    })
    .then(ret => {
      console.log(ret);
    }).catch(err => console.error(err));

程序挂起col.count命令。如果我删除readPreference选项，它可以正常工作。我的副本集读取首选项设置为primaryPrefered，如下所示：

rs1:PRIMARY> db.getMongo().getReadPref()
{ "mode" : "primaryPrefered" }

我不知道为什么secondary读取首选项会阻止我的应用程序。如何在我的应用程序中正确使用它？

以下是我的副本设置状态：

rs1:PRIMARY> rs.status()
{
    "set" : "rs1",
    "date" : ISODate("2018-04-13T01:06:49.269Z"),
    "myState" : 1,
    "term" : NumberLong(22),
    "heartbeatIntervalMillis" : NumberLong(2000),
    "optimes" : {
        "lastCommittedOpTime" : {
            "ts" : Timestamp(1523581602, 1),
            "t" : NumberLong(22)
        },
        "readConcernMajorityOpTime" : {
            "ts" : Timestamp(1523581602, 1),
            "t" : NumberLong(22)
        },
        "appliedOpTime" : {
            "ts" : Timestamp(1523581602, 1),
            "t" : NumberLong(22)
        },
        "durableOpTime" : {
            "ts" : Timestamp(1523581602, 1),
            "t" : NumberLong(22)
        }
    },
    "members" : [
        {
            "_id" : 0,
            "name" : "mongo1:37017",
            "health" : 1,
            "state" : 1,
            "stateStr" : "PRIMARY",
            "uptime" : 155084,
            "optime" : {
                "ts" : Timestamp(1523581602, 1),
                "t" : NumberLong(22)
            },
            "optimeDate" : ISODate("2018-04-13T01:06:42Z"),
            "electionTime" : Timestamp(1523537159, 1),
            "electionDate" : ISODate("2018-04-12T12:45:59Z"),
            "configVersion" : 199516,
            "self" : true
        },
        {
            "_id" : 1,
            "name" : "mongo2:37018",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 44550,
            "optime" : {
                "ts" : Timestamp(1523581602, 1),
                "t" : NumberLong(22)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1523581602, 1),
                "t" : NumberLong(22)
            },
            "optimeDate" : ISODate("2018-04-13T01:06:42Z"),
            "optimeDurableDate" : ISODate("2018-04-13T01:06:42Z"),
            "lastHeartbeat" : ISODate("2018-04-13T01:06:48.757Z"),
            "lastHeartbeatRecv" : ISODate("2018-04-13T01:06:48.756Z"),
            "pingMs" : NumberLong(0),
            "syncingTo" : "mongo1:37017",
            "configVersion" : 199516
        },
        {
            "_id" : 2,
            "name" : "mongo3:37019",
            "health" : 1,
            "state" : 2,
            "stateStr" : "SECONDARY",
            "uptime" : 44480,
            "optime" : {
                "ts" : Timestamp(1523581602, 1),
                "t" : NumberLong(22)
            },
            "optimeDurable" : {
                "ts" : Timestamp(1523581602, 1),
                "t" : NumberLong(22)
            },
            "optimeDate" : ISODate("2018-04-13T01:06:42Z"),
            "optimeDurableDate" : ISODate("2018-04-13T01:06:42Z"),
            "lastHeartbeat" : ISODate("2018-04-13T01:06:48.758Z"),
            "lastHeartbeatRecv" : ISODate("2018-04-13T01:06:48.757Z"),
            "pingMs" : NumberLong(0),
            "syncingTo" : "mongo2:37018",
            "configVersion" : 199516
        }
    ],
    "ok" : 1,
    "operationTime" : Timestamp(1523581602, 1)
}