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mongodb基础-索引
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1.索引介绍 mongodb的索引和我们遇到的rdbms的索引含义一样,原理也基本一样首先我们先在一个没有索引的集合上做一个查询,具体的查询计划可以通过explain()函数获取: db . t1 . find ({ username : user101 }). explain () { queryPlanner : { plannerVersion
1.索引介绍
mongodb的索引和我们遇到的rdbms的索引含义一样,原理也基本一样
首先我们先在一个没有索引的集合上做一个查询,具体的查询计划可以通过explain()函数获取:
> db.t1.find({"username":"user101"}).explain()
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "suq.t1",
"indexFilterSet" : false,
"parsedQuery" : {
"username" : {
"$eq" : "user101"
}
},
"winningPlan" : {
"stage" : "COLLSCAN",
"filter" : {
"username" : {
"$eq" : "user101"
}
},
"direction" : "forward"
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "mongodb1",
"port" : 27017,
"version" : "3.2.6",
"gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25"
},
"ok" : 1
}
如果要看详细的执行计划可以在explain添加executionStats或者allPlansExecution
> db.t1.find({"username":"user101"}).explain("allPlansExecution")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "suq.t1",
"indexFilterSet" : false,
"parsedQuery" : {
"username" : {
"$eq" : "user101"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"username" : 1
},
"indexName" : "username_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"username" : [
"[\"user101\", \"user101\"]"
]
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 0,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 1,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"username" : 1
},
"indexName" : "username_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"username" : [
"[\"user101\", \"user101\"]"
]
},
"keysExamined" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
},
"allPlansExecution" : [ ]
},
"serverInfo" : {
"host" : "mongodb1",
"port" : 27017,
"version" : "3.2.6",
"gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25"
},
"ok" : 1
}
这里的执行计划是collscan表示集合扫描,我们给文件username创建一个索引,使用db.collectionname.ensureIndex({"colname":[1/-1]})来创建 --新版本中使用createIndex来替换ensureIndex
其中1表示列的排序是从小大到排序,-1表示从大到小排序.
> db.t1.ensureIndex({"username":1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
<code class="lang
> db.t1.find({"username":"user101"}).explain()
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "suq.t1",
"indexFilterSet" : false,
"parsedQuery" : {
"username" : {
"$eq" : "user101"
}
},
"winningPlan" : {
"stage" : "COLLSCAN",
"filter" : {
"username" : {
"$eq" : "user101"
}
},
"direction" : "forward"
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "mongodb1",
"port" : 27017,
"version" : "3.2.6",
"gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25"
},
"ok" : 1
}
> db.t1.find({"username":"user101"}).explain("allPlansExecution")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "suq.t1",
"indexFilterSet" : false,
"parsedQuery" : {
"username" : {
"$eq" : "user101"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"username" : 1
},
"indexName" : "username_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"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,
"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" : {
"username" : 1
},
"indexName" : "username_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"username" : [
"[\"user101\", \"user101\"]"
]
},
"keysExamined" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
},
"allPlansExecution" : [ ]
},
"serverInfo" : {
"host" : "mongodb1",
"port" : 27017,
"version" : "3.2.6",
"gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25"
},
"ok" : 1
}
> db.t1.ensureIndex({"username":1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
<code class="lang
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