mongodb基础-索引

来源：知高教育

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,