【发布时间】：2014-08-30 21:08:10
【问题描述】：
我想问一下mongodb索引。我可以在查找和排序中使用不同的索引吗？例如，我有两个索引：
(a:-1)
(b:1,c:1)
什么索引使用了这句话？
({a:[$gt30}},{a:[$lt50}}]}.sort({c:1})
【问题讨论】：
标签： mongodb sorting indexing find
【发布时间】：2014-08-30 21:08:10
【问题描述】：
我可以在查找和排序中使用不同的索引吗？
阅读更多内容后，您将在文档页面底部看到关于索引交叉的内容：http://docs.mongodb.org/manual/core/index-intersection/#index-intersection-and-sort
当 sort() 操作需要与查询谓词完全分离的索引时，索引交集不适用。
所以不，即使 ypou 创建了 {c:1} 的索引，它也不能单独用于与 {a:1} 相交
什么索引使用了这句话？
在这种情况下，只会使用{a:1}。
【讨论】：
在称为单字段索引的单个字段上创建索引。
创建多个单字段索引来提高您的查询和排序性能不会有太大帮助！。您应该改用复合索引。
查看 MongoDB 上的文档：https://docs.mongodb.com/manual/core/index-compound/
如果您想了解如何为字段编制索引以及如何衡量查询的性能。
并在 Youtube 上查看本教程：https://dplink.app/nxLgvk7lR
【讨论】：
假设我正在收集具有以下文档的人员集合：
{
dob:
{ age : 50} ,
gender : "male" ,
phone : ""
}
现在我创建如下索引。
1 : db.persons.createIndex({"dob.age" : -1})
2 : db.persons.createIndex({phone : 1 , gender : 1})
- 现在如果我像你一样执行下面的查询
db.persons.explain("executionStats").find({$and : [ {"dob.age" : {$lt : 50} } , {"dob.age" : {$gt : 30} } ] } ).sort({gender : 1 })
我会得到以下执行统计数据：
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "college.persons",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"queryHash" : "22FEA299",
"planCacheKey" : "5E8F38C1",
"winningPlan" : {
"stage" : "SORT",
"sortPattern" : {
"phone" : 1
},
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"dob.age" : -1
},
"indexName" : "dob.age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"dob.age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"dob.age" : [
"(50.0, 30.0)"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1734,
"executionTimeMillis" : 10,
"totalKeysExamined" : 1734,
"totalDocsExamined" : 1734,
"executionStages" : {
"stage" : "SORT",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 3471,
"advanced" : 1734,
"needTime" : 1736,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"sortPattern" : {
"phone" : 1
},
"memUsage" : 1914799,
"memLimit" : 33554432,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 1736,
"advanced" : 1734,
"needTime" : 1,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"inputStage" : {
"stage" : "FETCH",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 1735,
"advanced" : 1734,
"needTime" : 0,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"docsExamined" : 1734,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 1735,
"advanced" : 1734,
"needTime" : 0,
"needYield" : 0,
"saveState" : 27,
"restoreState" : 27,
"isEOF" : 1,
"keyPattern" : {
"dob.age" : -1
},
"indexName" : "dob.age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"dob.age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"dob.age" : [
"(50.0, 30.0)"
]
},
"keysExamined" : 1734,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
}
}
},
"serverInfo" : {
"host" : "RGGYSLT-0483",
"port" : 27017,
"version" : "4.2.0",
"gitVersion" : "a4b751dcf51dd249c5865812b390cfd1c0129c30"
},
"ok" : 1
}
这意味着首先使用 IXScan 在单个字段上获取数据，然后对其进行排序 第三场分别。
但是，当我更改查询以对已创建索引的字段进行排序时，情况就会发生变化。现在 {"dob.age" : -1} 索引被拒绝。
在 Mongo db 中，Winning 计划是可以提前获取 100 个文档并且 Mongo db 缓存该计划以供查询的计划。现在，此缓存将在 1000 次文档插入、索引重建、服务器重新启动或新索引插入后被清除。
因此，将使用哪个索引取决于获胜计划。
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "college.persons",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"queryHash" : "DA8248FA",
"planCacheKey" : "E779554F",
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"gender" : 1,
"phone" : 1
},
"indexName" : "gender_1_phone_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"gender" : [ ],
"phone" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"gender" : [
"[MinKey, MaxKey]"
],
"phone" : [
"[MinKey, MaxKey]"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "SORT",
"sortPattern" : {
"gender" : 1,
"phone" : 1
},
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"dob.age" : -1
},
"indexName" : "dob.age_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"dob.age" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"dob.age" : [
"(50.0, 30.0)"
]
}
}
}
}
}
]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1734,
"executionTimeMillis" : 12,
"totalKeysExamined" : 5002,
"totalDocsExamined" : 5002,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"dob.age" : {
"$lt" : 50
}
},
{
"dob.age" : {
"$gt" : 30
}
}
]
},
"nReturned" : 1734,
"executionTimeMillisEstimate" : 0,
"works" : 5003,
"advanced" : 1734,
"needTime" : 3268,
"needYield" : 0,
"saveState" : 41,
"restoreState" : 41,
"isEOF" : 1,
"docsExamined" : 5002,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 5002,
"executionTimeMillisEstimate" : 0,
"works" : 5003,
"advanced" : 5002,
"needTime" : 0,
"needYield" : 0,
"saveState" : 41,
"restoreState" : 41,
"isEOF" : 1,
"keyPattern" : {
"gender" : 1,
"phone" : 1
},
"indexName" : "gender_1_phone_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"gender" : [ ],
"phone" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"gender" : [
"[MinKey, MaxKey]"
],
"phone" : [
"[MinKey, MaxKey]"
]
},
"keysExamined" : 5002,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
},
"serverInfo" : {
"host" : "RGGYSLT-0483",
"port" : 27017,
"version" : "4.2.0",
"gitVersion" : "a4b751dcf51dd249c5865812b390cfd1c0129c30"
},
"ok" : 1
}
【讨论】：