了解MongoDB查询计划
要在MongoDB中获取查询计划，请使用explain()。$explain运算符提供有关查询计划的信息。
让我们创建一个包含文档的集合-
> db.demo408.insertOne({"Value":50});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e70e3a115dc524f70227678")
}
> db.demo408.insertOne({"Value":20});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e70e3a715dc524f70227679")
}
> db.demo408.insertOne({"Value":45});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e70e3ac15dc524f7022767a")
}
> db.demo408.insertOne({"Value":35});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e70e3af15dc524f7022767b")
}
> db.demo408.createIndex({Value:1});
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}在find()方法的帮助下显示集合中的所有文档-
> db.demo408.find();
这将产生以下输出-
{ "_id" : ObjectId("5e70e3a115dc524f70227678"), "Value" : 50 }
{ "_id" : ObjectId("5e70e3a715dc524f70227679"), "Value" : 20 }
{ "_id" : ObjectId("5e70e3ac15dc524f7022767a"), "Value" : 45 }
{ "_id" : ObjectId("5e70e3af15dc524f7022767b"), "Value" : 35 }以下是查询以了解MongoDB中的查询计划-
> db.demo408.explain().find( { Value: { $gt: 40 } } );这将产生以下输出-
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.demo408",
"indexFilterSet" : false,
"parsedQuery" : {
"Value" : {
"$gt" : 40
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"Value" : 1
},
"indexName" : "Value_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"Value" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"Value" : [
"(40.0, inf.0]"
]
}
}
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "DESKTOP-QN2RB3H",
"port" : 27017,
"version" : "4.0.5",
"gitVersion" : "3739429dd92b92d1b0ab120911a23d50bf03c412"
},
"ok" : 1
}