MongoDB: สร้างระบบนับแท็ก (Tag Counting) บนข้อมูลใหญ่ด้วย Index + explain()

สร้างดัชนีและข้อมูลตัวอย่าง

> db.demo278.ensureIndex({"Subjects":1});
{ "createdCollectionAutomatically": true, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1 }
> db.demo278.insertOne({"Subjects":["MySQL","MongoDB","Java"]});
{ "acknowledged": true, "insertedId": ObjectId("5e49096edd099650a5401a55") }
> db.demo278.insertOne({"Subjects":["C","C++"]});
{ "acknowledged": true, "insertedId": ObjectId("5e490978dd099650a5401a56") }
> db.demo278.insertOne({"Subjects":["Spring","Hibernate"]});
{ "acknowledged": true, "insertedId": ObjectId("5e490984dd099650a5401a57") }

แสดงข้อมูล

> db.demo278.find();

{ "_id": ObjectId("5e49096edd099650a5401a55"), "Subjects": [ "MySQL", "MongoDB", "Java" ] }
{ "_id": ObjectId("5e490978dd099650a5401a56"), "Subjects": [ "C", "C++" ] }
{ "_id": ObjectId("5e490984dd099650a5401a57"), "Subjects": [ "Spring", "Hibernate" ] }

ตรวจสอบ Performance ด้วย explain()

> db.demo278.find({Subjects:{$in:["Spring","MongoDB"]}}).explain();

ผลลัพธ์: ใช้ Index "Subjects_1" แบบ MultiKey (IXSCAN)

{
  "queryPlanner": {
    "plannerVersion": 1,
    "namespace": "test.demo278",
    "indexFilterSet": false,
    "parsedQuery": {
      "Subjects": { "$in": [ "MongoDB", "Spring" ] }
    },
    "winningPlan": {
      "stage": "FETCH",
      "inputStage": {
        "stage": "IXSCAN",
        "keyPattern": { "Subjects": 1 },
        "indexName": "Subjects_1",
        "isMultiKey": true,
        "multiKeyPaths": { "Subjects": [ "Subjects" ] },
        "isUnique": false,
        "isSparse": false,
        "isPartial": false,
        "indexVersion": 2,
        "direction": "forward",
        "indexBounds": {
          "Subjects": [ "["MongoDB", "MongoDB"]", "["Spring", "Spring"]" ]
        }
      }
    },
    "rejectedPlans": []
  },
  "serverInfo": { "host": "DESKTOP-QN2RB3H", "port": 27017, "version": "4.0.5", "gitVersion": "3739429dd92b92d1b0ab120911a23d50bf03c412" },
  "ok": 1
}