为什么我在主分片上出现网络错误？

Question

我有两个集合，即'scanner'和'applicationinfo'。 两者都没有伤害。 当我在主分片上运行以下查询时：

db.scans.aggregate(
    [
        {
            $match:{
                "customerId":500,
                "startTime":{
                    $gte:1568073600000
                },
                "endTime":{
                    $lte:1568160000000
                }
            }
        },
        {
            $lookup:{
                "from":"applicationinfo",
                "let":{
                    "sha":"$sha"
                },
                "pipeline":[
                    {
                        $match:{
                            "customerId":500,
                            $expr:{
                                $eq:["$sha256","$$sha"]
                            }
                        }
                    },
                    {
                        $sort:{
                            "_id":-1
                        }
                    },
                    {
                        $limit:1
                    },
                    {
                        $project:{
                            "_id":0
                        }
                    }
                ],
                "as":"applicationinfoLookup"
            }
        }
    ],
    {
        "allowDiskUse":true
    }
).pretty()

它抛出错误：

2019-09-11T11:23:30.379+0000 E QUERY    [js] Error: error doing query: failed: network error while attempting to run command 'aggregate' on host '127.0.0.1:27001'  :
DB.prototype.runCommand@src/mongo/shell/db.js:168:1
DB.prototype.runReadCommand@src/mongo/shell/db.js:139:16
DB.prototype._runAggregate/doAgg<@src/mongo/shell/db.js:239:60
DB.prototype._runAggregate@src/mongo/shell/db.js:242:21
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1056:12

当对mongos触发相同的查询时，将引发以下错误：

2019-09-11T11:51:53.743+0530 E QUERY    [js] Error: command failed: {
    "ok" : 0,
    "errmsg" : "Could not find host matching read preference { mode: \"primary\" } for set 1",
    "code" : 133,
    "codeName" : "FailedToSatisfyReadPreference",
    "operationTime" : Timestamp(1568182910, 1),
    "$clusterTime" : {
        "clusterTime" : Timestamp(1568182910, 1),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }
} : aggregate failed :
_geterrorwithcode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:18:14
_assertcommandworked@src/mongo/shell/assert.js:534:17
assert.commandworked@src/mongo/shell/assert.js:618:16
db.prototype._runaggregate@src/mongo/shell/db.js:260:9
dbcollection.prototype.aggregate@src/mongo/shell/collection.js:1062:12
@(shell):1:1

奇怪的是，当我从查找管道中删除最后一个投影阶段时，查询运行顺利。