MongoDB executionStats理解

我目前正在尝试将索引集成到我的一个集合中。我所有的测试都成功了，我真的可以看到扫描文件的改进数量等等，但是我的一个结果有点奇怪，或者可能我没有很好地理解它。 你能给我解释一下吗

我有一个所有者/持有人/产品的集合，这里是一个例子，同时也是相关文件的集合：

{
    "_id": ObjectId("59ef7c84f545c8278c8cd967"),
    "owner": "59ef7c83f545c8278c8cd965",
    "holder": "59ef7c84f545c8278c8cd967",
    "product": 1,
    "date" : ISODate("2017-10-24T17:46:44.367Z")
}

以下是索引：

{
        "v" : 1,
        "key" : {
                "_id" : 1
        },
        "name" : "_id_",
        "ns" : "mydb.relation"
},
{
        "v" : 1,
        "key" : {
                "owner" : 1
        },
        "name" : "onlyOwner",
        "ns" : "mydb.relation"
},
{
        "v" : 1,
        "key" : {
                "holder" : 1
        },
        "name" : "onlyHolder",
        "ns" : "mydb.relation"
},
{
        "v" : 1,
        "key" : {
                "owner" : 1,
                "holder" : 1
        },
        "name" : "ownerAndHolder",
        "ns" : "mydb.relation"
},
{
        "v" : 1,
        "key" : {
                "owner" : 1,
                "product" : 1
        },
        "name" : "ownerAndProduct",
        "ns" : "mydb.relation"
}

我执行了以下查询：

db.relation.find({ $and : [{"owner" : "59ef7c83f545c8278c8cd965"}, {"holder" : "59ef7c84f545c8278c8cd967"}]})

我的亲戚很好地回报了前面提到的那一位。所以我决定检查executionStats以查看状态，结果如下：

{
        "queryPlanner" : {
                "plannerVersion" : 1,
                "namespace" : "mydb.relation",
                "indexFilterSet" : false,
                "parsedQuery" : {
                        "$and" : [
                                {
                                        "holder" : {
                                                "$eq" : "59ef7c84f545c8278c8cd967"
                                        }
                                },
                                {
                                        "owner" : {
                                                "$eq" : "59ef7c83f545c8278c8cd965"
                                        }
                                }
                        ]
                },
                "winningPlan" : {
                        "stage" : "FETCH",
                        "filter" : {
                                "holder" : {
                                        "$eq" : "59ef7c84f545c8278c8cd967"
                                }
                        },
                        "inputStage" : {
                                "stage" : "IXSCAN",
                                "keyPattern" : {
                                        "owner" : 1,
                                        "product" : 1
                                },
                                "indexName" : "ownerAndProduct",
                                "isMultiKey" : false,
                                "multiKeyPaths" : {
                                        "owner" : [ ],
                                        "product" : [ ]
                                },
                                "isUnique" : false,
                                "isSparse" : false,
                                "isPartial" : false,
                                "indexVersion" : 1,
                                "direction" : "forward",
                                "indexBounds" : {
                                        "owner" : [
                                                "[\"59ef7c83f545c8278c8cd965\", \"59ef7c83f545c8278c8cd965\"]"
                                        ],
                                        "product" : [
                                                "[MinKey, MaxKey]"
                                        ]
                                }
                        }
                },
                "rejectedPlans" : [
                        {
                                "stage" : "FETCH",
                                "inputStage" : {
                                        "stage" : "IXSCAN",
                                        "keyPattern" : {
                                                "owner" : 1,
                                                "holder" : 1
                                        },
                                        "indexName" : "ownerAndHolder",
                                        "isMultiKey" : false,
                                        "multiKeyPaths" : {
                                                "owner" : [ ],
                                                "holder" : [ ]
                                        },
                                        "isUnique" : false,
                                        "isSparse" : false,
                                        "isPartial" : false,
                                        "indexVersion" : 1,
                                        "direction" : "forward",
                                        "indexBounds" : {
                                                "owner" : [
                                                        "[\"59ef7c83f545c8278c8cd965\", \"59ef7c83f545c8278c8cd
                                                ],
                                                "holder" : [
                                                        "[\"59ef7c84f545c8278c8cd967\", \"59ef7c84f545c8278c8cd
                                                ]
                                        }
                                }
                        },
                        {
                                "stage" : "FETCH",
                                "filter" : {
                                        "holder" : {
                                                "$eq" : "59ef7c84f545c8278c8cd967"
                                        }
                                },
                                "inputStage" : {
                                        "stage" : "IXSCAN",
                                        "keyPattern" : {
                                                "owner" : 1
                                        },
                                        "indexName" : "onlyOwner",
                                        "isMultiKey" : false,
                                        "multiKeyPaths" : {
                                                "owner" : [ ]
                                        },
                                        "isUnique" : false,
                                        "isSparse" : false,
                                        "isPartial" : false,
                                        "indexVersion" : 1,
                                        "direction" : "forward",
                                        "indexBounds" : {
                                                "owner" : [
                                                        "[\"59ef7c83f545c8278c8cd965\", \"59ef7c83f545c8278c8cd
                                                ]
                                        }
                                }
                        },
                        {
                                "stage" : "FETCH",
                                "filter" : {
                                        "owner" : {
                                                "$eq" : "59ef7c83f545c8278c8cd965"
                                        }
                                },
                                "inputStage" : {
                                        "stage" : "IXSCAN",
                                        "keyPattern" : {
                                                "holder" : 1
                                        },
                                        "indexName" : "onlyHolder",
                                        "isMultiKey" : false,
                                        "multiKeyPaths" : {
                                                "holder" : [ ]
                                        },
                                        "isUnique" : false,
                                        "isSparse" : false,
                                        "isPartial" : false,
                                        "indexVersion" : 1,
                                        "direction" : "forward",
                                        "indexBounds" : {
                                                "holder" : [
                                                        "[\"59ef7c84f545c8278c8cd967\", \"59ef7c84f545c8278c8cd
                                                ]
                                        }
                                }
                        }
                ]
        },
        "executionStats" : {
                "executionSuccess" : true,
                "nReturned" : 1,
                "executionTimeMillis" : 0,
                "totalKeysExamined" : 1,
                "totalDocsExamined" : 1,
                "executionStages" : {
                        "stage" : "FETCH",
                        "filter" : {
                                "holder" : {
                                        "$eq" : "59ef7c84f545c8278c8cd967"
                                }
                        },
                        "nReturned" : 1,
                        "executionTimeMillisEstimate" : 0,
                        "works" : 3,
                        "advanced" : 1,
                        "needTime" : 0,
                        "needYield" : 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,
                                "needYield" : 0,
                                "saveState" : 0,
                                "restoreState" : 0,
                                "isEOF" : 1,
                                "invalidates" : 0,
                                "keyPattern" : {
                                        "owner" : 1,
                                        "product" : 1
                                },
                                "indexName" : "ownerAndProduct",
                                "isMultiKey" : false,
                                "multiKeyPaths" : {
                                        "owner" : [ ],
                                        "product" : [ ]
                                },
                                "isUnique" : false,
                                "isSparse" : false,
                                "isPartial" : false,
                                "indexVersion" : 1,
                                "direction" : "forward",
                                "indexBounds" : {
                                        "owner" : [
                                                "[\"59ef7c83f545c8278c8cd965\", \"59ef7c83f545c8278c8cd965\"]"
                                        ],
                                        "product" : [
                                                "[MinKey, MaxKey]"
                                        ]
                                },
                                "keysExamined" : 1,
                                "seeks" : 1,
                                "dupsTested" : 0,
                                "dupsDropped" : 0,
                                "seenInvalidated" : 0
                        }
                }
        },
        "serverInfo" : {
                "host" : "NCEL15605",
                "port" : 27017,
                "version" : "3.4.6",
                "gitVersion" : "c55eb86ef46ee7aede3b1e2a5d184a7df4bfb5b5"
        },
        "ok" : 1
}

因此，我理解onlyHolder onlyOwner被拒绝，但我不理解为什么拒绝ownerAndHolder并使用ownerAndProduct，因为我没有将其用作变量

有人能帮我理解这个结果吗？从发现的答案是正确的，但是这是我不理解的MongoDB的选择

提前谢谢

---

关于

看看这两个字段：

"nReturned" : 1,
"totalDocsExamined" : 1,

这意味着Mongo只需检查一份文档就可以返回一份。然后，所选择的查询计划，尽管与直觉相反，却获得了可能的最佳结果。看起来至少有一个其他计划可以达到与所有者持股人指数相同的结果。在这种情况下，Mongo可以自由选择计划

如果您想了解查询优化的详细信息，请阅读本文