Question

我试图通过对嵌套对象数组进行查找查询来获取集合中的一些文档。嵌套对象已建立索引，但find查询未使用索引来获取文档。

这是文档的结构。

    "_id" : ObjectId("5bc6498c1ec4062983c4f4ef"),
    "appId" : ObjectId("5bbc775036021bea06d9bbc2"),

    "status" : "active",


    "segmentations" : [ 
       {
            "name" : "ch-1",
            "values" : [ 
                'true'
            ],
            "type" : "string"
        },
        {
            "name" : "browerInfo",
            "values" : [ 
                "Firefox"
            ],
            "version" : [ 
                "62.0"
            ],
            "majorVersion" : [ 
                "62"
            ],
            "type" : "string"
        }, 
        {
            "name" : "OS",
            "values" : [ 
                "Ubuntu"
            ],
            "type" : "string"
        }, 
        {
            "name" : "lastVisitTime",
            "values" : [ 
                1539721615231.0
            ],
            "type" : "number"
        }
    ]
}

这是索引字段。

    {
        "v" : 2,
        "key" : {
            "appId" : 1,
            "status" : 1,
            "segmentations.name" : 1,
            "segmentations.values" : 1
        },
        "name" : "SEGMENT_INDEX",
        "ns" : "test.Collname"
    }

下面是我正在执行的查找查询



db.Collname.find({
    appId: ObjectId("5c6a8ef544ff62c73bdb98fc"),
    "segmentations.name": 'ch-1',
    'segmentations.values': 'true',


    status: 'active'
}, {})

我试图使用

获取查询执行信息。

<above query>.explain("executionStats")

结果是

{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "test.Collname",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "$and" : [ 
                {
                    "appId" : {
                        "$eq" : ObjectId("5c6a8ef544ff62c73bdb98fc")
                    }
                }, 
                {
                    "segmentations.name" : {
                        "$eq" : "ch-1"
                    }
                }, 
                {
                    "segmentations.values" : {
                        "$eq" : "true"
                    }
                }, 
                {
                    "status" : {
                        "$eq" : "active"
                    }
                }
            ]
        },
        "winningPlan" : {
            "stage" : "FETCH",
            "filter" : {
                "segmentations.values" : {
                    "$eq" : "true"
                }
            },
            "inputStage" : {
                "stage" : "IXSCAN",
                "keyPattern" : {
                    "appId" : 1.0,
                    "status" : 1.0,
                    "segmentations.name" : 1.0,
                    "segmentations.values" : 1.0
                },
                "indexName" : "SEGMENT_INDEX",
                "isMultiKey" : true,
                "multiKeyPaths" : {
                    "appId" : [],
                    "status" : [],
                    "segmentations.name" : [ 
                        "segmentations"
                    ],
                    "segmentations.values" : [ 
                        "segmentations", 
                        "segmentations.values"
                    ]
                },
                "isUnique" : false,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : 2,
                "direction" : "forward",
                "indexBounds" : {
                    "appId" : [ 
                        "[ObjectId('5c6a8ef544ff62c73bdb98fc'), ObjectId('5c6a8ef544ff62c73bdb98fc')]"
                    ],
                    "status" : [ 
                        "[\"active\", \"active\"]"
                    ],
                    "segmentations.name" : [ 
                        "[\"ch-1\", \"ch-1\"]"
                    ],
                    "segmentations.values" : [ 
                        "[MinKey, MaxKey]"
                    ]
                }
            }
        },
        "rejectedPlans" : []
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : 28176,
        "executionTimeMillis" : 72,
        "totalKeysExamined" : 28176,
        "totalDocsExamined" : 28176,
        "executionStages" : {
            "stage" : "FETCH",
            "filter" : {
                "segmentations.values" : {
                    "$eq" : "true"
                }
            },
            "nReturned" : 28176,
            "executionTimeMillisEstimate" : 70,
            "works" : 28177,
            "advanced" : 28176,
            "needTime" : 0,
            "needYield" : 0,
            "saveState" : 220,
            "restoreState" : 220,
            "isEOF" : 1,
            "invalidates" : 0,
            "docsExamined" : 28176,
            "alreadyHasObj" : 0,
            "inputStage" : {
                "stage" : "IXSCAN",
                "nReturned" : 28176,
                "executionTimeMillisEstimate" : 10,
                "works" : 28177,
                "advanced" : 28176,
                "needTime" : 0,
                "needYield" : 0,
                "saveState" : 220,
                "restoreState" : 220,
                "isEOF" : 1,
                "invalidates" : 0,
                "keyPattern" : {
                    "appId" : 1.0,
                    "status" : 1.0,
                    "segmentations.name" : 1.0,
                    "segmentations.values" : 1.0
                },
                "indexName" : "SEGMENT_INDEX",
                "isMultiKey" : true,
                "multiKeyPaths" : {
                    "appId" : [],
                    "status" : [],
                    "segmentations.name" : [ 
                        "segmentations"
                    ],
                    "segmentations.values" : [ 
                        "segmentations", 
                        "segmentations.values"
                    ]
                },
                "isUnique" : false,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : 2,
                "direction" : "forward",
                "indexBounds" : {
                    "appId" : [ 
                        "[ObjectId('5c6a8ef544ff62c73bdb98fc'), ObjectId('5c6a8ef544ff62c73bdb98fc')]"
                    ],
                    "status" : [ 
                        "[\"active\", \"active\"]"
                    ],
                    "segmentations.name" : [ 
                        "[\"ch-1\", \"ch-1\"]"
                    ],
                    "segmentations.values" : [ 
                        "[MinKey, MaxKey]"
                    ]
                },
                "keysExamined" : 28176,
                "seeks" : 1,
                "dupsTested" : 28176,
                "dupsDropped" : 0,
                "seenInvalidated" : 0
            }
        }
    },
    "serverInfo" : {
        "host" : "sys3029",
        "port" : 27017,
        "version" : "4.0.9",
        "gitVersion" : "fc525e2d9b0e4bceff5c2201457e564362909765"
    },
    "ok" : 1.0
}

我从executionStats可以看到，在“ IXSCAN”阶段未使用“ segmentations.values”字段。在“ segmentations.values”上有一个额外的过滤器阶段。 IXSCAN阶段仅花费10毫秒，而FILTER阶段仅花费50毫秒。

我不明白为什么该字段未包含在IXSCAN阶段中。我的收藏集中有大约320万个文档，由于这个问题，查询的执行时间比预期的要长。

请帮助我解决此问题。预先谢谢你。

请建议我如果我需要更改数据库结构，如果在mongodb中不可能，则可以建议其他支持上述操作的数据库。

Answer 1

以下查询将对两个数组字段都使用索引：

.find({
    appId: ObjectId("5c6a8ef544ff62c73bdb98fc"),
    segmentations:{$elemMatch:{name: 'ch-1',values: 'true'}},
    status: 'active'
}, {})

如果您不是使用$ elemMatch，则MongoDB可以使用 “ segmentations.name” 或< /strong>“segmentations.values”的边界，但不能同时使用两者。为了将“ segmentations.name”的边界与“ segmentations.values”的边界进行复合，查询必须使用$ elemMatch。

要将来自同一数组的索引键的边界组合在一起：

索引键必须共享相同的字段路径，但不包括字段名称，

并且查询必须在字段上指定谓词在该路径上使用$ elemMatch。

我建议您阅读有关multikey-index-bounds以及有关$elemMatch的mongodb文档。

Mongodb未将索引用于对象数组

1 个答案: