What does config shard mean here?

by abc   Last Updated August 14, 2019 10:06 AM

I created a MongoDB sharded cluster with replica set rsa, rsb and rsc. Configuration server replica set is configRS. Initially shard status listed only these shards as primary shard for the sharded databases. But now I can see an other shard "config" listed. Where did this shard come from? What does it mean?

 [[email protected] 1]#  mongo --port 27777 --host 172.16.66.74 -u cv_user -p'xxxxx' --authenticationDatabase 'admin' --eval "db.adminCommand( { listDatabases: 1 } )"
    MongoDB shell version v3.6.6
    connecting to: mongodb://172.16.66.74:27777/
    MongoDB server version: 3.6.6
    {
        "databases" : [
            {
                    "name" : "admin",
                    "sizeOnDisk" : 147456,
                    "empty" : false,
                    "shards" : {
                            "config" : 147456
                    }
            },
            {
                    "name" : "config",
                    "sizeOnDisk" : 1228800,
                    "empty" : false,
                    "shards" : {
                            "rsa" : 200704,
                            "rsb" : 102400,
                            "rsc" : 118784,
                            "config" : 806912
                    }
            },
            {
                    "name" : "test",
                    "sizeOnDisk" : 32768,
                    "empty" : false,
                    "shards" : {
                            "rsb" : 32768
                    }
            }
        ],
        "totalSize" : 1409024,
        "totalSizeMb" : 1,
        "ok" : 1,
        "$clusterTime" : {
            "clusterTime" : Timestamp(1565775023, 1),
            "signature" : {
                    "hash" : BinData(0,"vIxGUfXD3ZzE5gkr5wSHDBwJuSg="),
                    "keyId" : NumberLong("6721659792886071315")
            }
        },
        "operationTime" : Timestamp(1565775023, 1)
    }

Shard status

mongos> sh.status()
--- Sharding Status ---
  sharding version: {
    "_id" : 1,
    "minCompatibleVersion" : 5,
    "currentVersion" : 6,
    "clusterId" : ObjectId("5d4821f8ffb408d9b4ea389a")
  }
  shards:
        {  "_id" : "rsa",  "host" : "rsa/172.16.63.8:27000",  "state" : 1 }
        {  "_id" : "rsb",  "host" : "rsb/172.16.66.74:27000",  "state" : 1 }
        {  "_id" : "rsc",  "host" : "rsc/172.16.73.51:27001",  "state" : 1 }
  active mongoses:
        "3.6.6" : 1
  autosplit:
        Currently enabled: yes
  balancer:
        Currently enabled:  yes
        Currently running:  yes
        Failed balancer rounds in last 5 attempts:  5
        Last reported error:  Could not find host matching read preference { mode: "primary" } for set rsa
        Time of Reported error:  Wed Aug 14 2019 15:14:01 GMT+0530 (IST)
        Migration Results for the last 24 hours:
                No recent migrations
  databases:
        {  "_id" : "config",  "primary" : "config",  "partitioned" : true }
                config.system.sessions
                        shard key: { "_id" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                rsa     1
                        { "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : rsa Timestamp(1, 0)
        {  "_id" : "test",  "primary" : "rsb",  "partitioned" : false }
Tags : mongodb sharding


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