@koshi_life です。
MongoDB v4 explain 結果をちゃんと理解してクエリ改善 (前半:explain結果の見方) の続きです。
今回の記事内容
本記事では、396,416件をフルスキャンしていた以下クエリ(平均実行時間 851.6ms)の速度改善を行います。前提条件やテストデータについては 前回記事を参考。
対象のクエリ
ありがちな1ユーザの最新投稿３件を取得するクエリを改善対象とします。
mongo> db.qiita_items.find({'user_id':'koshilife'},{'_id':0,'created_at':1,'title':1,'url':1}).sort({'created_at':-1}).limit(3) { "title" : "MongoDB Aggregation 100本ノック 前半 (group, sort, limit, project)", "url" : "https://qiita.com/koshilife/items/422070ee6aa636fb75fc", "created_at" : ISODate("2019-04-15T11:52:57Z") } { "title" : "Mongoid 特定Collectionにのみインデックスを作る", "url" : "https://qiita.com/koshilife/items/140b5a66d5fa6d1e7ee1", "created_at" : ISODate("2019-04-14T15:06:26Z") } { "title" : "Google Sheets API v4「1セル 50000文字までの制限あるよ」", "url" : "https://qiita.com/koshilife/items/5aff56c1bb9e5d31067f", "created_at" : ISODate("2019-04-08T01:31:04Z") }
TL;DR
- 走査レコードが少ないほど実行時間が短くなる。(傾向あり)
- 複合フィールドの定義順は大事。走査レコード数が変わるので。[^1]
- 検証したデータ量では複合フィールドのソート順(昇順、降順)は実行速度に寄与しなかった。[^2]
[^1]: 複合フィールドの定義順は大事と公式にも記載あり。Doc
[^2]: ソート順 単一フィールドは関係ないが複合フィールドのインデックスは関係あるらしいDoc
Btreeを頭に思い浮かべてIndexを貼る感じで上手に貼れるようになる気がしている。
以下記事が参考になった。
インデックス検証パターン
- v1: user_idのみ単一インデックス
{user_id: 1} - v2: user_id/created_at(降順)の複合インデックス
{user_id: 1, created_at: -1} - v3: user_id/created_at(昇順)の複合インデックス
{user_id: 1, created_at: 1} - v4: created_at(降順)/user_idの複合インデックス
{created_at: -1, user_id: 1} - v5: 複数インデックスが存在 v1~v4 全て登録済み
検証結果
| 検証パターン | 走査レコード totalDocsExamined |
実行時間(平均) | 時間(1) | 時間(2) | 時間(3) | 時間(4) | 時間(5) | インデックスサイズ | 備考 |
|---|---|---|---|---|---|---|---|---|---|
| v1 | 45 | 2.2 | 2 | 3 | 5 | 0 | 1 | 2.67 MB | |
| v2 | 3 | 0.6 | 2 | 0 | 0 | 1 | 0 | 5.45 MB | v2,v3,v5誤差かと |
| v3 | 3 | 0.2 | 1 | 0 | 0 | 0 | 0 | 5.45 MB | v2,v3,v5誤差かと |
| v4 | 4,806 | 38.8 | 52 | 53 | 20 | 46 | 23 | 8.74 MB | |
| v5 | 3 | 0.4 | 0 | 0 | 0 | 1 | 1 | - | v2のIndexが採択された |
| インデックスなし | 396,416 | 851.6 | 951 | 636 | 914 | 893 | 864 | - |
※時間の単位はms
参考:各インデックス作成文
// v1
mongo> db.qiita_items.createIndex({user_id: 1}, {unique: false})
// v2
mongo> db.qiita_items.createIndex({user_id: 1, created_at: -1 }, {unique: false})
// v3
mongo> db.qiita_items.createIndex({user_id: 1, created_at: 1}, {unique: false})
// v4
mongo> db.qiita_items.createIndex({created_at: -1, user_id: 1}, {unique: false})
参考:explain結果
v1 {user_id: 1}
mongo> db.qiita_items.find({'user_id':'koshilife'},{'_id':0,'created_at':1,'title':1,'url':1}).sort({'created_at':-1}).limit(3).explain('executionStats')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "qiita_api_development.qiita_items",
"indexFilterSet" : false,
"parsedQuery" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"winningPlan" : {
"stage" : "PROJECTION",
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "SORT",
"sortPattern" : {
"created_at" : -1
},
"limitAmount" : 3,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"user_id" : 1
},
"indexName" : "user_id_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
]
}
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 3,
"executionTimeMillis" : 26,
"totalKeysExamined" : 45,
"totalDocsExamined" : 45,
"executionStages" : {
"stage" : "PROJECTION",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 51,
"advanced" : 3,
"needTime" : 47,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "SORT",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 51,
"advanced" : 3,
"needTime" : 47,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"sortPattern" : {
"created_at" : -1
},
"memUsage" : 1041,
"memLimit" : 33554432,
"limitAmount" : 3,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"nReturned" : 45,
"executionTimeMillisEstimate" : 0,
"works" : 47,
"advanced" : 45,
"needTime" : 1,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"inputStage" : {
"stage" : "FETCH",
"nReturned" : 45,
"executionTimeMillisEstimate" : 0,
"works" : 46,
"advanced" : 45,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 45,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 45,
"executionTimeMillisEstimate" : 0,
"works" : 46,
"advanced" : 45,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"user_id" : 1
},
"indexName" : "user_id_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
]
},
"keysExamined" : 45,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
}
}
},
"serverInfo" : {
"host" : "KenjinoMacBook-Air.local",
"port" : 27017,
"version" : "4.0.3",
"gitVersion" : "7ea530946fa7880364d88c8d8b6026bbc9ffa48c"
},
"ok" : 1
}
v2 {user_id: 1, created_at: -1}
mongo> db.qiita_items.find({'user_id':'koshilife'},{'_id':0,'created_at':1,'title':1,'url':1}).sort({'created_at':-1}).limit(3).explain('executionStats')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "qiita_api_development.qiita_items",
"indexFilterSet" : false,
"parsedQuery" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"winningPlan" : {
"stage" : "LIMIT",
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"user_id" : 1,
"created_at" : -1
},
"indexName" : "user_id_1_created_at_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ],
"created_at" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
],
"created_at" : [
"[MaxKey, MinKey]"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 3,
"executionTimeMillis" : 1,
"totalKeysExamined" : 3,
"totalDocsExamined" : 3,
"executionStages" : {
"stage" : "LIMIT",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 4,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 0,
"invalidates" : 0,
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 3,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"user_id" : 1,
"created_at" : -1
},
"indexName" : "user_id_1_created_at_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ],
"created_at" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
],
"created_at" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 3,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
}
},
"serverInfo" : {
"host" : "KenjinoMacBook-Air.local",
"port" : 27017,
"version" : "4.0.3",
"gitVersion" : "7ea530946fa7880364d88c8d8b6026bbc9ffa48c"
},
"ok" : 1
}
v3 {user_id: 1, created_at: 1}
mongo> db.qiita_items.find({'user_id':'koshilife'},{'_id':0,'created_at':1,'title':1,'url':1}).sort({'created_at':-1}).limit(3).explain('executionStats')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "qiita_api_development.qiita_items",
"indexFilterSet" : false,
"parsedQuery" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"winningPlan" : {
"stage" : "LIMIT",
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"user_id" : 1,
"created_at" : 1
},
"indexName" : "user_id_1_created_at_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ],
"created_at" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "backward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
],
"created_at" : [
"[MaxKey, MinKey]"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 3,
"executionTimeMillis" : 1,
"totalKeysExamined" : 3,
"totalDocsExamined" : 3,
"executionStages" : {
"stage" : "LIMIT",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 4,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 0,
"invalidates" : 0,
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 3,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 3,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 3,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"user_id" : 1,
"created_at" : 1
},
"indexName" : "user_id_1_created_at_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ],
"created_at" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "backward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
],
"created_at" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 3,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
}
},
"serverInfo" : {
"host" : "KenjinoMacBook-Air.local",
"port" : 27017,
"version" : "4.0.3",
"gitVersion" : "7ea530946fa7880364d88c8d8b6026bbc9ffa48c"
},
"ok" : 1
}
v4 {created_at: -1, user_id: 1}
mongo> db.qiita_items.find({'user_id':'koshilife'},{'_id':0,'created_at':1,'title':1,'url':1}).sort({'created_at':-1}).limit(3).explain('executionStats')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "qiita_api_development.qiita_items",
"indexFilterSet" : false,
"parsedQuery" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"winningPlan" : {
"stage" : "LIMIT",
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"created_at" : -1,
"user_id" : 1
},
"indexName" : "created_at_-1_user_id_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"created_at" : [ ],
"user_id" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"created_at" : [
"[MaxKey, MinKey]"
],
"user_id" : [
"[MinKey, MaxKey]"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 3,
"executionTimeMillis" : 21,
"totalKeysExamined" : 4806,
"totalDocsExamined" : 4806,
"executionStages" : {
"stage" : "LIMIT",
"nReturned" : 3,
"executionTimeMillisEstimate" : 10,
"works" : 4807,
"advanced" : 3,
"needTime" : 4803,
"needYield" : 0,
"saveState" : 37,
"restoreState" : 37,
"isEOF" : 1,
"invalidates" : 0,
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"nReturned" : 3,
"executionTimeMillisEstimate" : 10,
"works" : 4806,
"advanced" : 3,
"needTime" : 4803,
"needYield" : 0,
"saveState" : 37,
"restoreState" : 37,
"isEOF" : 0,
"invalidates" : 0,
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"nReturned" : 3,
"executionTimeMillisEstimate" : 10,
"works" : 4806,
"advanced" : 3,
"needTime" : 4803,
"needYield" : 0,
"saveState" : 37,
"restoreState" : 37,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 4806,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 4806,
"executionTimeMillisEstimate" : 10,
"works" : 4806,
"advanced" : 4806,
"needTime" : 0,
"needYield" : 0,
"saveState" : 37,
"restoreState" : 37,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"created_at" : -1,
"user_id" : 1
},
"indexName" : "created_at_-1_user_id_1",
"isMultiKey" : false,
"multiKeyPaths" : {
"created_at" : [ ],
"user_id" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"created_at" : [
"[MaxKey, MinKey]"
],
"user_id" : [
"[MinKey, MaxKey]"
]
},
"keysExamined" : 4806,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
}
},
"serverInfo" : {
"host" : "KenjinoMacBook-Air.local",
"port" : 27017,
"version" : "4.0.3",
"gitVersion" : "7ea530946fa7880364d88c8d8b6026bbc9ffa48c"
},
"ok" : 1
}
v5 v1~v4 全て登録済み
rejectedPlans が初めて登場し、最良のIndexを判断している様子がわかる。
mongo> db.qiita_items.find({'user_id':'koshilife'},{'_id':0,'created_at':1,'title':1,'url':1}).sort({'created_at':-1}).limit(3).explain('executionStats')
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "qiita_api_development.qiita_items",
"indexFilterSet" : false,
"parsedQuery" : {
"user_id" : {
"$eq" : "koshilife"
}
},
"winningPlan" : {
"stage" : "LIMIT",
"limitAmount" : 3,
"inputStage" : {
"stage" : "PROJECTION",
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"user_id" : 1,
"created_at" : -1
},
"indexName" : "user_id_1_created_at_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"user_id" : [ ],
"created_at" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[\"koshilife\", \"koshilife\"]"
],
"created_at" : [
"[MaxKey, MinKey]"
]
}
}
}
}
},
"rejectedPlans" : [
{
"stage" : "PROJECTION",
"transformBy" : {
"_id" : 0,
"created_at" : 1,
"title" : 1,
"url" : 1
},
"inputStage" : {
"stage" : "SORT",
"sortPattern" : {
"created_at" : -1
},
"limitAmount" : 3,
"inputStage" : {
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