MongoDB ——explain查询分析
程振濂
测试数据：
/* 1 */
{
"_id" : ObjectId("5ca0538159aa1df98e31c634"),
"numIndex" : 0.0
}
/* 2 */
{
"_id" : ObjectId("5ca0538159aa1df98e31c635"),
"numIndex" : 1.0
}
// 写入了三万条这样的numIndex自增1的数据
分析语句：
db.getCollection('student').find({numIndex:{"$gt":50,"$lt":55}}).explain("executionStats")
分析结果：
/* 1 */
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "testdb.student",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"numIndex" : {
"$lt" : 55.0
}
},
{
"numIndex" : {
"$gt" : 50.0
}
}
]
},
"winningPlan" : {
"stage" : "COLLSCAN",
"filter" : {
"$and" : [
{
"numIndex" : {
"$lt" : 55.0
}
},
{
"numIndex" : {
"$gt" : 50.0
}
}
]
},
"direction" : "forward"
},
"rejectedPlans" : []
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 4,
"executionTimeMillis" : 20,
"totalKeysExamined" : 0,
"totalDocsExamined" : 30000,
"executionStages" : {
"stage" : "COLLSCAN",
"filter" : {
"$and" : [
{
"numIndex" : {
"$lt" : 55.0
}
},
{
"numIndex" : {
"$gt" : 50.0
}
}
]
},
"nReturned" : 4,
"executionTimeMillisEstimate" : 10,
"works" : 30002,
"advanced" : 4,
"needTime" : 29997,
"needYield" : 0,
"saveState" : 234,
"restoreState" : 234,
"isEOF" : 1,
"invalidates" : 0,
"direction" : "forward",
"docsExamined" : 30000
}
},
"serverInfo" : {
"host" : "localhost",
"port" : 27017,
"version" : "4.0.0",
"gitVersion" : "3b07af3d4f471ae89e8186d33bbb1d5259597d51"
},
"ok" : 1.0
}
感觉mongo的查询分析比sql的好看一点儿。上面是具体的查询的语句，下面是执行结果集服务器信息。
totalDocsExamined:检索总行数
totalKeysExamined:显示整个扫描的索引数量
nReturned：返回了几行
之后我们再来创建索引看看：
db.getCollection('student').createIndex({numIndex:1})
看下我们现在都有哪些索引：
db.getCollection('student').getIndexes()
返回结果：
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "testdb.student"
},
{
"v" : 2,
"key" : {
"numIndex" : 1.0
},
"name" : "numIndex_1",
"ns" : "testdb.student"
}
]
再执行下刚才的查询：
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "testdb.student",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"numIndex" : {
"$lt" : 55.0
}
},
{
"numIndex" : {
"$gt" : 50.0
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"numIndex" : 1.0
},
"indexName" : "numIndex_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"numIndex" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"numIndex" : [
"(50.0, 55.0)"
]
}
}
},
"rejectedPlans" : []
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 4,
"executionTimeMillis" : 5,
"totalKeysExamined" : 4,
"totalDocsExamined" : 4,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 4,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 4,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 4,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 4,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 4,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"numIndex" : 1.0
},
"indexName" : "numIndex_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"numIndex" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"numIndex" : [
"(50.0, 55.0)"
]
},
"keysExamined" : 4,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
"serverInfo" : {
"host" : "localhost",
"port" : 27017,
"version" : "4.0.0",
"gitVersion" : "3b07af3d4f471ae89e8186d33bbb1d5259597d51"
},
"ok" : 1.0
}
这时候，我们使用上了索引："indexName" : "numIndex_1" ，executionTimeMillis 从20降低到了5。
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