mongodb 3.0 中怎么显示cursor和nscanned？

Question

如题
这是我用explain显示出来的数据

> db.users.explain("allPlansExecution").find({username:'user101'})
{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "test.users",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "username" : {
                "$eq" : "user101"
            }
        },
        "winningPlan" : {
            "stage" : "FETCH",
            "inputStage" : {
                "stage" : "IXSCAN",
                "keyPattern" : {
                    "username" : 1
                },
                "indexName" : "username_1",
                "isMultiKey" : false,
                "direction" : "forward",
                "indexBounds" : {
                    "username" : [
                        "[\"user101\", \"user101\"]"
                    ]
                }
            }
        },
        "rejectedPlans" : [ ]
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : 1,
        "executionTimeMillis" : 0,
        "totalKeysExamined" : 1,
        "totalDocsExamined" : 1,
        "executionStages" : {
            "stage" : "FETCH",
            "nReturned" : 1,
            "executionTimeMillisEstimate" : 0,
            "works" : 2,
            "advanced" : 1,
            "needTime" : 0,
            "needFetch" : 0,
            "saveState" : 0,
            "restoreState" : 0,
            "isEOF" : 1,
            "invalidates" : 0,
            "docsExamined" : 1,
            "alreadyHasObj" : 0,
            "inputStage" : {
                "stage" : "IXSCAN",
                "nReturned" : 1,
                "executionTimeMillisEstimate" : 0,
                "works" : 2,
                "advanced" : 1,
                "needTime" : 0,
                "needFetch" : 0,
                "saveState" : 0,
                "restoreState" : 0,
                "isEOF" : 1,
                "invalidates" : 0,
                "keyPattern" : {
                    "username" : 1
                },
                "indexName" : "username_1",
                "isMultiKey" : false,
                "direction" : "forward",
                "indexBounds" : {
                    "username" : [
                        "[\"user101\", \"user101\"]"
                    ]
                },
                "keysExamined" : 1,
                "dupsTested" : 0,
                "dupsDropped" : 0,
                "seenInvalidated" : 0,
                "matchTested" : 0
            }
        },
        "allPlansExecution" : [ ]
    },
    "serverInfo" : {
        "host" : "mongo2",
        "port" : 27017,
        "version" : "3.0.0",
        "gitVersion" : "a841fd6394365954886924a35076691b4d149168"
    },
    "ok" : 1
}

Answer 1

Saya baru sahaja menyemak dokumentasi, dan saya menyalahkan diri sendiri kerana tidak melihat keputusan dengan teliti. .

queryPlanner.winningPlan.inputStage.stageStrategi pertanyaan paparan lajur
- IXSCAN bermaksud menggunakan Indeks untuk bertanya
- COLLSCAN bermaksud menggunakan pertanyaan lajur, iaitu membandingkan masa lalu satu demi satu

Nama indeks dalam

cursor telah dialihkan ke queryPlanner.winningPlan.inputStage.indexName

Dalam 3.0, executionStats.totalDocsExamined digunakan untuk memaparkan jumlah dokumen yang perlu disemak, menggantikan nscanned.

Answer 2

>db.person.find({age:{$lt:20}}).explain("executionStats")
        "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : 20,
        "executionTimeMillis" : 567,
        "totalKeysExamined" : 0,
        "totalDocsExamined" : 1000000,
        "executionStages" : {
            "stage" : "COLLSCAN",
            "filter" : {
                "age" : {
                    "$lt" : 20
                }
            },
            "nReturned" : 20,
            "executionTimeMillisEstimate" : 520,
            "works" : 1000002,
            "advanced" : 20,
            "needTime" : 999981,
            "needFetch" : 0,
            "saveState" : 7812,
            "restoreState" : 7812,
            "isEOF" : 1,
            "invalidates" : 0,
            "direction" : "forward",
            "docsExamined" : 1000000
        }