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MongoDB学习之Explain执行计划

来源：SegmentFault

时间：2023-02-16 15:40:13 288浏览收藏

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db.collection.find().explain(verbose)

{
  "queryPlanner":{
    "plannerVersion":1,
    "namespace":"mock.users",
    "indexFilterSet":false,
    "parsedQuery":{
      "age":{
        "$gte":10
      }
    },
    "winningPlan":{
      "stage":"FETCH",
      "inputStage":{
        "stage":"IXSCAN",
        "keyPattern":{
          "age":1,
          "username":1
        },
        "indexName":"age_1_username_1",
        "isMultiKey":false,
        "multiKeyPaths":{
          "age":[
          ],
          "username":[
          ]
        },
        "isUnique":false,
        "isSparse":false,
        "isPartial":false,
        "indexVersion":2,
        "direction":"forward",
        "indexBounds":{
          "age":[
            "[10, inf.0]"
          ],
          "username":[
            "[MinKey, MaxKey]"
          ]
        }
      }
    },
    "rejectedPlans":[
      {
        "stage":"FETCH",
        "inputStage":{
          "stage":"IXSCAN",
          "keyPattern":{
            "age":1
          },
          "indexName":"age_1",
          "isMultiKey":false,
          "multiKeyPaths":{
            "age":[
            ]
          },
          "isUnique":false,
          "isSparse":false,
          "isPartial":false,
          "indexVersion":2,
          "direction":"forward",
          "indexBounds":{
            "age":[
              "[10, inf.0]"
            ]
          }
        }
      }
    ]
  },
  "executionStats":{   --这个集合是executionStats&allPlansExecution模式才有的
    "executionSuccess":true,
    "nReturned":680520,
    "executionTimeMillis":1121,
    "totalKeysExamined":680520,
    "totalDocsExamined":680520,
    "executionStages":{
      "stage":"FETCH",
      "nReturned":680520,
      "executionTimeMillisEstimate":143,
      "works":680521,
      "advanced":680520,
      "needTime":0,
      "needYield":0,
      "saveState":680,
      "restoreState":680,
      "isEOF":1,
      "docsExamined":680520,
      "alreadyHasObj":0,
      "inputStage":{
        "stage":"IXSCAN",
        "nReturned":680520,
        "executionTimeMillisEstimate":43,
        "works":680521,
        "advanced":680520,
        "needTime":0,
        "needYield":0,
        "saveState":680,
        "restoreState":680,
        "isEOF":1,
        "keyPattern":{
          "age":1,
          "username":1
        },
        "indexName":"age_1_username_1",
        "isMultiKey":false,
        "multiKeyPaths":{
          "age":[
          ],
          "username":[
          ]
        },
        "isUnique":false,
        "isSparse":false,
        "isPartial":false,
        "indexVersion":2,
        "direction":"forward",
        "indexBounds":{
          "age":[
            "[10, inf.0]"
          ],
          "username":[
            "[MinKey, MaxKey]"
          ]
        },
        "keysExamined":680520,
        "seeks":1,
        "dupsTested":0,
        "dupsDropped":0
      }
    },
    "allPlansExecution":[  --这是allPlansExecution执行才会有的返回集合
      {
        "nReturned":101,
        "executionTimeMillisEstimate":0,
        "totalKeysExamined":101,
        "totalDocsExamined":101,
        "executionStages":{
          .......
        }
      }
    ]
  },
  "serverInfo":{
    "host":"supman",
    "port":27017,
    "version":"4.4.10",
    "gitVersion":"58971da1ef93435a9f62bf4708a81713def6e88c"
  },
  "ok":1
}

详解

db.users.createIndex({"username":1},{unique:true"})

db.users.createIndex({"email":1},{sparse:true"})

db.users.createIndex({age:1},{partialFilterExpression:{age:{"$gte":25}}})

如上，这种索引只在查询条件为

db.users.find().sort()         --这种情况是forward
db.users.find().sort({age:-1}) --这种情况是backward

```
indexVersion
```
索引版本
```
indexBounds
```
所扫描的索引范围,例如
```
indexBounds: { age: [ '[36, 38]' ] } } }
```
就是代表扫描
```
[36,38]
```
这个区间的
```
age
```
字段的索引
```
rejectedPlans
```
拒绝计划,非最优的执行计划，它的字段与
```
winningPlan
```
一样不再描述
- .......