nscanned_mongos

gistfile1.txt

db['collection_name'].find({
  $maxScan:500000,
  $explain:true,
  $query:{
    "$and":[
      {
        "$or":[
          {"_id":"NOvRVdV0ru"},
          {"deviceIds":"id123"}
        ]
      },
      {
        "_id":{
          "$nin":["e8tFeJW797"]
        }
      }
    ],
    "permission":{"$in":[null,"*"]}
  }
})

{
  "server": "db126:27017",
  "allPlans": [
    {
      "indexBounds": {
        "permission": [
          [ null, null ],
          [ "*", "*" ]
        ]
      },
      "nscanned": 500001,
      "nscannedObjects": 500000,
      "n": 0,
      "cursor": "BtreeCursor permission_1 multi"
    }
  ],
  "indexBounds": {
    "permission": [
      [ null, null ],
      [ "*", "*" ]
    ]
  },
  "millis": 15339,
  "nChunkSkips": 0,
  "nYields": 737,
  "indexOnly": false,
  "cursor": "BtreeCursor permission_1 multi",
  "isMultiKey": false,
  "n": 0,
  "nscannedObjects": 500000,
  "nscanned": 500001,
  "nscannedObjectsAllPlans": 500000,
  "nscannedAllPlans": 500001,
  "scanAndOrder": false
}



db['collection_name'].find({
  $maxScan:500000,
  $explain:true,
  $query:{
    "$and":[
      {
        "$or":[
          {"_id":"NOvRVdV0ru"},
          {"deviceIds":"id123"}
        ]
      },
      {"_id":{"$nin":["e8tFeJW797"]}},
      {"permission":{"$in":[null,"*"]}}
    ]
  }
})

{
  "server": "db126:27017",
  "allPlans": [
    {
      "indexBounds": {
        "permission": [
          [ null, null ],
          [ "*", "*" ]
        ]
      },
      "nscanned": 500001,
      "nscannedObjects": 500000,
      "n": 0,
      "cursor": "BtreeCursor permission_1 multi"
    }
  ],
  "indexBounds": {
    "permission": [
      [ null, null ],
      [ "*", "*" ]
    ]
  },
  "millis": 13665,
  "nChunkSkips": 0,
  "nYields": 648,
  "indexOnly": false,
  "cursor": "BtreeCursor permission_1 multi",
  "isMultiKey": false,
  "n": 0,
  "nscannedObjects": 500000,
  "nscanned": 500001,
  "nscannedObjectsAllPlans": 500000,
  "nscannedAllPlans": 500001,
  "scanAndOrder": false
}


==GOOD CASE==
db['collection_name'].find({
  $maxScan:500000,
  $explain:true,
  $query:{
    "$or":[
      {"_id":"NOvRVdV0ru","deviceIds":"id123"}
    ],
    "_id":{"$nin":["e8tFeJW797"]},
    "permission":{"$in":[null,"*"]}
  }
})

{
  "server": "db007:27017",
  "allPlans": [
    {
      "indexBounds": {
        "_id": [
          [ "NOvRVdV0ru", "NOvRVdV0ru" ]
        ]
      },
      "nscanned": 1,
      "nscannedObjects": 1,
      "n": 1,
      "cursor": "BtreeCursor _id_"
    },
    {
      "indexBounds": {
        "deviceIds": [
          [ "id123", "id123" ]
        ]
      },
      "nscanned": 1,
      "nscannedObjects": 1,
      "n": 1,
      "cursor": "BtreeCursor deviceIds_1"
    },
    {
      "indexBounds": {
        "permission": [
          [ null, null ],
          [ "*", "*" ]
        ]
      },
      "nscanned": 1,
      "nscannedObjects": 1,
      "n": 0,
      "cursor": "BtreeCursor permission_1 multi"
    },
    {
      "indexBounds": {},
      "nscanned": 1,
      "nscannedObjects": 1,
      "n": 0,
      "cursor": "BasicCursor"
    }
  ],
  "indexBounds": {
    "_id": [
      [ "NOvRVdV0ru", "NOvRVdV0ru" ]
    ]
  },
  "millis": 0,
  "nChunkSkips": 0,
  "nYields": 0,
  "indexOnly": false,
  "cursor": "BtreeCursor _id_",
  "isMultiKey": false,
  "n": 1,
  "nscannedObjects": 1,
  "nscanned": 1,
  "nscannedObjectsAllPlans": 4,
  "nscannedAllPlans": 4,
  "scanAndOrder": false
}