Database 为什么MongoDB不使用复合索引进行查询？
以下是我为该集合提供的复合索引和单一索引：Database 为什么MongoDB不使用复合索引进行查询？,database,mongodb,indexing,Database,Mongodb,Indexing,以下是我为该集合提供的复合索引和单一索引： ///db.Collection.getIndexes() /* 1 */ { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "service.Collection" }, /* 2 */ {
///db.Collection.getIndexes()
/* 1 */
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "service.Collection"
},
/* 2 */
{
"v" : 2,
"key" : {
"FirstId" : 1,
"SecondId" : 1,
"CreationTime" : -1
},
"name" : "FirstIdSecondIdCreationTime",
"collation" : {
"locale" : "en",
"caseLevel" : false,
"caseFirst" : "off",
"strength" : 1,
"numericOrdering" : false,
"alternate" : "non-ignorable",
"maxVariable" : "punct",
"normalization" : false,
"backwards" : false,
"version" : "57.1"
},
"ns" : "service.Collection"
},
/* 3 */
{
"v" : 2,
"key" : {
"CreationTime" : 1
},
"name" : "CreationTime",
"collation" : {
"locale" : "en",
"caseLevel" : false,
"caseFirst" : "off",
"strength" : 1,
"numericOrdering" : false,
"alternate" : "non-ignorable",
"maxVariable" : "punct",
"normalization" : false,
"backwards" : false,
"version" : "57.1"
},
"ns" : "service.Collection"
}
firstIDSecondCreationTime///service.Collection.find({ FirstId: "771367b7-4bef-49ab-bda1-6230254c6349", ///SecondId: "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f" })
/// .projection({})
/// .sort({_id:-1}).hint("FirstIdSecondIdCreationTime").explain('executionStats')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "service.Collection",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"FirstId" : {
"$eq" : "771367b7-4bef-49ab-bda1-6230254c6349"
}
},
{
"SecondId" : {
"$eq" : "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f"
}
}
]
},
"winningPlan" : {
"stage" : "SORT",
"sortPattern" : {
"_id" : -1
},
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"FirstId" : {
"$eq" : "771367b7-4bef-49ab-bda1-6230254c6349"
}
},
{
"SecondId" : {
"$eq" : "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f"
}
}
]
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"FirstId" : 1,
"SecondId" : 1,
"CreationTime" : -1
},
"indexName" : "FirstIdSecondIdCreationTime",
"collation" : {
"locale" : "en",
"caseLevel" : false,
"caseFirst" : "off",
"strength" : 1,
"numericOrdering" : false,
"alternate" : "non-ignorable",
"maxVariable" : "punct",
"normalization" : false,
"backwards" : false,
"version" : "57.1"
},
"isMultiKey" : false,
"multiKeyPaths" : {
"FirstId" : [ ],
"SecondId" : [ ],
"CreationTime" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"FirstId" : [
"[MinKey, MaxKey]"
],
"SecondId" : [
"[MinKey, MaxKey]"
],
"CreationTime" : [
"[MaxKey, MinKey]"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 5491,
"totalKeysExamined" : 856730,
"totalDocsExamined" : 856730,
"executionStages" : {
"stage" : "SORT",
"nReturned" : 1,
"executionTimeMillisEstimate" : 5261,
"works" : 856734,
"advanced" : 1,
"needTime" : 856732,
"needYield" : 0,
"saveState" : 6697,
"restoreState" : 6697,
"isEOF" : 1,
"invalidates" : 0,
"sortPattern" : {
"_id" : -1
},
"memUsage" : 432,
"memLimit" : 33554432,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"nReturned" : 1,
"executionTimeMillisEstimate" : 5201,
"works" : 856732,
"advanced" : 1,
"needTime" : 856730,
"needYield" : 0,
"saveState" : 6697,
"restoreState" : 6697,
"isEOF" : 1,
"invalidates" : 0,
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"FirstId" : {
"$eq" : "771367b7-4bef-49ab-bda1-6230254c6349"
}
},
{
"SecondId" : {
"$eq" : "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f"
}
}
]
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 5131,
"works" : 856731,
"advanced" : 1,
"needTime" : 856729,
"needYield" : 0,
"saveState" : 6697,
"restoreState" : 6697,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 856730,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 856730,
"executionTimeMillisEstimate" : 820,
"works" : 856731,
"advanced" : 856730,
"needTime" : 0,
"needYield" : 0,
"saveState" : 6697,
"restoreState" : 6697,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"FirstId" : 1,
"SecondId" : 1,
"CreationTime" : -1
},
"indexName" : "FirstIdSecondIdCreationTime",
"collation" : {
"locale" : "en",
"caseLevel" : false,
"caseFirst" : "off",
"strength" : 1,
"numericOrdering" : false,
"alternate" : "non-ignorable",
"maxVariable" : "punct",
"normalization" : false,
"backwards" : false,
"version" : "57.1"
},
"isMultiKey" : false,
"multiKeyPaths" : {
"FirstId" : [ ],
"SecondId" : [ ],
"CreationTime" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"FirstId" : [
"[MinKey, MaxKey]"
],
"SecondId" : [
"[MinKey, MaxKey]"
],
"CreationTime" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 856730,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0,
"indexDef" : {
"indexName" : "FirstIdSecondIdCreationTime",
"isMultiKey" : false,
"multiKeyPaths" : {
"FirstId" : [ ],
"SecondId" : [ ],
"CreationTime" : [ ]
},
"keyPattern" : {
"FirstId" : 1,
"SecondId" : 1,
"CreationTime" : -1
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"direction" : "forward"
}
}
}
}
}
"event": {
"dataset": "mongodb.log",
"module": "mongodb"
},
"service": {
"type": "mongodb"
},
"message": "command service.Collection command: find { find: \"Collection\",
filter: { FirstId: \"771367b7-4bef-49ab-bda1-6230254c6349\", SecondId: \"3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f\" }, sort: { CreationTime: -1 }, limit: 1,
planSummary: COLLSCAN keysExamined:0 docsExamined:784787 hasSortStage:1 cursorExhausted:1 numYields:6175 nreturned:1 reslen:677
locks:{ Global: { acquireCount: { r: 12352 } }, Database: { acquireCount: { r: 6176 } }, Collection: { acquireCount: { r: 6176 } } } protocol:op_msg 8441ms",
"mongodb.docsExamined": 784787,
"fileset": {
"name": "log"
},
firstIDSecondCreationTime根据评论中的建议，我已经运行了
explain（“allPlansExecution”）能否请您按前导索引（即firstId、secondId和creationTime）按相同顺序排序，并查看是否使用索引。它将给出前导索引字段是否也应该排序的想法。没有自动考虑“FirstIDSecondCreationTime”索引，因为它是使用排序规则创建的，并且查询在运行时没有排序规则 使用游标方法为查询指定与索引相同的排序规则 使用该索引的5.5秒运行时间也相当慢。
如果您在
{FirstId:1，SecondId:1，{u id:1}allPlansExecution所有计划执行的结果，我猜获胜的计划是通过第一个id
和第二个id
进行筛选，并按\u id
排序？为什么一句话都没有提到firstIDSecondCreationTime
？这个计划甚至都没有实施……谢谢你的建议！以下是和的结果，它们工作得太好了（0ms）：。我不知道我将如何使用这些信息，现在我已经做到了。。。查询执行器可以使用索引*满足排序*而不是内存排序，这是什么意思？如果索引中的键按照相等排序范围排序，即索引包含要查询的字段以及要排序的字段，并且查询匹配离散值的字段位于索引规范中的排序字段之前，查询执行器可以保证扫描索引将找到已排序顺序的文档，因此它可以完全跳过内存中的排序阶段。看看这个
///db.Collection.find({ FirstId: "771367b7-4bef-49ab-bda1-6230254c6349", ///SecondId: "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f" })
/// .projection({})
/// .sort({_id:-1}).explain('allPlansExecution')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "service.Collection",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"FirstId" : {
"$eq" : "771367b7-4bef-49ab-bda1-6230254c6349"
}
},
{
"SecondId" : {
"$eq" : "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f"
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"FirstId" : {
"$eq" : "771367b7-4bef-49ab-bda1-6230254c6349"
}
},
{
"SecondId" : {
"$eq" : "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f"
}
}
]
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"_id" : 1
},
"indexName" : "_id_",
"isMultiKey" : false,
"multiKeyPaths" : {
"_id" : [ ]
},
"isUnique" : true,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "backward",
"indexBounds" : {
"_id" : [
"[MaxKey, MinKey]"
]
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 5408,
"totalKeysExamined" : 856748,
"totalDocsExamined" : 856748,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"FirstId" : {
"$eq" : "771367b7-4bef-49ab-bda1-6230254c6349"
}
},
{
"SecondId" : {
"$eq" : "3bffb3cd-fb5e-43e5-abd1-e0b48c97f78f"
}
}
]
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 4862,
"works" : 856749,
"advanced" : 1,
"needTime" : 856747,
"needYield" : 0,
"saveState" : 6694,
"restoreState" : 6694,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 856748,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 856748,
"executionTimeMillisEstimate" : 1220,
"works" : 856749,
"advanced" : 856748,
"needTime" : 0,
"needYield" : 0,
"saveState" : 6694,
"restoreState" : 6694,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"_id" : 1
},
"indexName" : "_id_",
"isMultiKey" : false,
"multiKeyPaths" : {
"_id" : [ ]
},
"isUnique" : true,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "backward",
"indexBounds" : {
"_id" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 856748,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
},
"allPlansExecution" : [ ]
}
}