标签：exp 情况 rect iso class 扫描 article 解释 tag
1:分析查询性能(Analyze Query Performance)通常使用执行计划(解释计划,explain Plan)来查询的情况，如查询耗费的时间，是否基于索引查询等.
那么,通常,我们想知道，建立的索引是否有效,效果如何，都需要通过执行计划查看。
语法:
db.collection.find(query,options).explain(options)
--------------------------------------------------------------------
#根据userid查询数据的情况
db.comment.find({userid:"1003"}).explain()
执行:
> db.comment.find({userid:"1003"})
{ "_id" : "3", "articleid" : "100003", "content" : "我爱你，绩憨憨3", "userid" : "1003", "nickname" : "hanhan", "createdatetime" : ISODate("2020-02-28T14:45:54.235Z"), "likenum" : 10, "state" : null }
> db.comment.find({userid:"1003"}).explain()
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "comment.comment",
"indexFilterSet" : false,
"parsedQuery" : {
"userid" : {
"$eq" : "1003"
}
},
"queryHash" : "37A12FC3",
"planCacheKey" : "37A12FC3",
"winningPlan" : {
"stage" : "COLLSCAN", #集合扫描，全部扫描
"filter" : {
"userid" : {
"$eq" : "1003"
}
},
"direction" : "forward"
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "LAPTOP-ZJ",
"port" : 27017,
"version" : "4.2.3",
"gitVersion" : "6874650b362138df74be53d366bbefc321ea32d4"
},
"ok" : 1
}
#加上索引，看效果
db.comment.createIndex({userid:1})
> db.comment.createIndex({userid:1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.comment.find({userid:"1003"}).explain({})
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "comment.comment",
"indexFilterSet" : false,
"parsedQuery" : {
"userid" : {
"$eq" : "1003"
}
},
"winningPlan" : {
"stage" : "FETCH", #这里是FETCH,拉取，有用了索引
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"userid" : 1
},
"indexName" : "userid_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"userid" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"userid" : [
"[\"1003\", \"1003\"]"
]
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 3,
"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,
"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,
"keyPattern" : {
"userid" : 1
},
"indexName" : "userid_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"userid" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"userid" : [
"[\"1003\", \"1003\"]"
]
},
"keysExamined" : 1,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
},
"allPlansExecution" : [ ]
},
"serverInfo" : {
"host" : "LAPTOP-ZJ",
"port" : 27017,
"version" : "4.2.3",
"gitVersion" : "6874650b362138df74be53d366bbefc321ea32d4"
},
"ok" : 1
}
#先通过IXSCAN,再FETCH
标签：exp 情况 rect iso class 扫描 article 解释 tag
原文地址：https://www.cnblogs.com/zhoujun007/p/12388907.html
