深入学习MongoDB之索引与执行计划
mongodb索引
创建索引:
db.getCollection("test").ensureIndex({"name":1});
或者db.getCollection("test").createIndex({"name":1});
{
"raw" : {
"shard3/192.168.3.18:20004,192.168.3.3:10004" : {
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1.0,
"$gleStats" : {
"lastOpTime" : Timestamp(6577988859047444, 1),
"electionId" : ObjectId("5b48c90f0000000000001c96")
}
}
},
"ok" : 1.0
}
索引创建成功;
查询索引状态
db.getCollection("test").getIndexes({"name":1});
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "dev.test"
},
{
"v" : 1,
"key" : {
"name" : 1.0
},
"name" : "name_1",
"ns" : "dev.test"
}
]
可以看到_id索引(默认的),和name索引
删除索引
db.getCollection("test").dropIndex({"name":1});
删除结果
{
"raw" : {
"shard3/192.168.3.18:20004,192.168.3.3:10004" : {
"nIndexesWas" : 2,
"ok" : 1.0,
"$gleStats" : {
"lastOpTime" : Timestamp(6577989129630384, 1),
"electionId" : ObjectId("5b48c90f0000000000001c96")
}
}
},
"ok" : 1.0
}
再次查询
db.getCollection("test").getIndexes({"name":1});
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "dev.test"
}
]
索引删除成功;
再次创建索引,并查看执行计划;
db.getCollection("test").ensureIndex({"name":1});
db.getCollection("test").find({name:"张三"}).explain();
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard3",
"connectionString" : "shard3/192.168.3.18:20004,192.168.3.3:10004",
"serverInfo" : {
"host" : "8ef2e84b1b94",
"port" : 27017,
"version" : "3.2.0",
"gitVersion" : "45d947729a0315accb6d4f15a6b06be6d9c19fe7"
},
"plannerVersion" : 1,
"namespace" : "dev.test",
"indexFilterSet" : false,
"parsedQuery" : {
"name" : {
"$eq" : "张三"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
}
}
},
"rejectedPlans" : []
}
]
}
},
"ok" : 1.0
}
通过winningPlan的"stage" : "FETCH",可以判断使用了索引,
另外可以给explain添加参数,查看更多的执行计划;
db.getCollection("test").find({name:"张三"}).explain("executionStats");
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard3",
"connectionString" : "shard3/192.168.3.18:20004,192.168.3.3:10004",
"serverInfo" : {
"host" : "8ef2e84b1b94",
"port" : 27017,
"version" : "3.2.0",
"gitVersion" : "45d947729a0315accb6d4f15a6b06be6d9c19fe7"
},
"plannerVersion" : 1,
"namespace" : "dev.test",
"indexFilterSet" : false,
"parsedQuery" : {
"name" : {
"$eq" : "张三"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
}
}
},
"rejectedPlans" : []
}
]
}
},
"executionStats" : {
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"executionStages" : {
"stage" : "SINGLE_SHARD",
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"totalChildMillis" : NumberLong(0),
"shards" : [
{
"shardName" : "shard3",
"executionSuccess" : true,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 2,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
},
"keysExamined" : 2,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
]
}
},
"ok" : 1.0
}
"executionStats"表示执行状态,
totalKeysExamined表示用到的索引数,如果这个值为0,则说明未使用到索引,
totalDocsExamined表示扫描的文档书
rejectedPlans代表弃用的索引,当前关于name的索引只有一个,所以弃用所以为null,
我们添加一个name和age的联合索引:
db.getCollection("test").ensureIndex({"name":1,"age":1});
在执行查询计划:
db.getCollection("test").find({name:"张三"}).explain("executionStats");
/* 1 */
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard3",
"connectionString" : "shard3/192.168.3.18:20004,192.168.3.3:10004",
"serverInfo" : {
"host" : "8ef2e84b1b94",
"port" : 27017,
"version" : "3.2.0",
"gitVersion" : "45d947729a0315accb6d4f15a6b06be6d9c19fe7"
},
"plannerVersion" : 1,
"namespace" : "dev.test",
"indexFilterSet" : false,
"parsedQuery" : {
"name" : {
"$eq" : "张三"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0,
"age" : 1.0
},
"indexName" : "name_1_age_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
],
"age" : [
"[MinKey, MaxKey]"
]
}
}
}
]
}
]
}
},
"executionStats" : {
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"executionStages" : {
"stage" : "SINGLE_SHARD",
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"totalChildMillis" : NumberLong(0),
"shards" : [
{
"shardName" : "shard3",
"executionSuccess" : true,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 4,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 2,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
},
"keysExamined" : 2,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
]
}
},
"ok" : 1.0
}
发现了弃用索引;
可以使用hint()指定使用的索引:
db.getCollection("test").find({name:"张三"}).hint({name:1,age:1}).explain("executionStats");
必须注意的是hint字段的顺序必须和已创建的索引保持一致
创建索引:
db.getCollection("test").ensureIndex({"name":1});
或者db.getCollection("test").createIndex({"name":1});
{
"raw" : {
"shard3/192.168.3.18:20004,192.168.3.3:10004" : {
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1.0,
"$gleStats" : {
"lastOpTime" : Timestamp(6577988859047444, 1),
"electionId" : ObjectId("5b48c90f0000000000001c96")
}
}
},
"ok" : 1.0
}
索引创建成功;
查询索引状态
db.getCollection("test").getIndexes({"name":1});
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "dev.test"
},
{
"v" : 1,
"key" : {
"name" : 1.0
},
"name" : "name_1",
"ns" : "dev.test"
}
]
可以看到_id索引(默认的),和name索引
删除索引
db.getCollection("test").dropIndex({"name":1});
删除结果
{
"raw" : {
"shard3/192.168.3.18:20004,192.168.3.3:10004" : {
"nIndexesWas" : 2,
"ok" : 1.0,
"$gleStats" : {
"lastOpTime" : Timestamp(6577989129630384, 1),
"electionId" : ObjectId("5b48c90f0000000000001c96")
}
}
},
"ok" : 1.0
}
再次查询
db.getCollection("test").getIndexes({"name":1});
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "dev.test"
}
]
索引删除成功;
再次创建索引,并查看执行计划;
db.getCollection("test").ensureIndex({"name":1});
db.getCollection("test").find({name:"张三"}).explain();
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard3",
"connectionString" : "shard3/192.168.3.18:20004,192.168.3.3:10004",
"serverInfo" : {
"host" : "8ef2e84b1b94",
"port" : 27017,
"version" : "3.2.0",
"gitVersion" : "45d947729a0315accb6d4f15a6b06be6d9c19fe7"
},
"plannerVersion" : 1,
"namespace" : "dev.test",
"indexFilterSet" : false,
"parsedQuery" : {
"name" : {
"$eq" : "张三"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
}
}
},
"rejectedPlans" : []
}
]
}
},
"ok" : 1.0
}
通过winningPlan的"stage" : "FETCH",可以判断使用了索引,
另外可以给explain添加参数,查看更多的执行计划;
db.getCollection("test").find({name:"张三"}).explain("executionStats");
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard3",
"connectionString" : "shard3/192.168.3.18:20004,192.168.3.3:10004",
"serverInfo" : {
"host" : "8ef2e84b1b94",
"port" : 27017,
"version" : "3.2.0",
"gitVersion" : "45d947729a0315accb6d4f15a6b06be6d9c19fe7"
},
"plannerVersion" : 1,
"namespace" : "dev.test",
"indexFilterSet" : false,
"parsedQuery" : {
"name" : {
"$eq" : "张三"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
}
}
},
"rejectedPlans" : []
}
]
}
},
"executionStats" : {
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"executionStages" : {
"stage" : "SINGLE_SHARD",
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"totalChildMillis" : NumberLong(0),
"shards" : [
{
"shardName" : "shard3",
"executionSuccess" : true,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 2,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
},
"keysExamined" : 2,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
]
}
},
"ok" : 1.0
}
"executionStats"表示执行状态,
totalKeysExamined表示用到的索引数,如果这个值为0,则说明未使用到索引,
totalDocsExamined表示扫描的文档书
rejectedPlans代表弃用的索引,当前关于name的索引只有一个,所以弃用所以为null,
我们添加一个name和age的联合索引:
db.getCollection("test").ensureIndex({"name":1,"age":1});
在执行查询计划:
db.getCollection("test").find({name:"张三"}).explain("executionStats");
/* 1 */
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard3",
"connectionString" : "shard3/192.168.3.18:20004,192.168.3.3:10004",
"serverInfo" : {
"host" : "8ef2e84b1b94",
"port" : 27017,
"version" : "3.2.0",
"gitVersion" : "45d947729a0315accb6d4f15a6b06be6d9c19fe7"
},
"plannerVersion" : 1,
"namespace" : "dev.test",
"indexFilterSet" : false,
"parsedQuery" : {
"name" : {
"$eq" : "张三"
}
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"name" : 1.0,
"age" : 1.0
},
"indexName" : "name_1_age_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
],
"age" : [
"[MinKey, MaxKey]"
]
}
}
}
]
}
]
}
},
"executionStats" : {
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"executionStages" : {
"stage" : "SINGLE_SHARD",
"nReturned" : 2,
"executionTimeMillis" : 1,
"totalKeysExamined" : 2,
"totalDocsExamined" : 2,
"totalChildMillis" : NumberLong(0),
"shards" : [
{
"shardName" : "shard3",
"executionSuccess" : true,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 4,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 2,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 2,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 2,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"name" : 1.0
},
"indexName" : "name_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"张三\", \"张三\"]"
]
},
"keysExamined" : 2,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
]
}
},
"ok" : 1.0
}
发现了弃用索引;
可以使用hint()指定使用的索引:
db.getCollection("test").find({name:"张三"}).hint({name:1,age:1}).explain("executionStats");
必须注意的是hint字段的顺序必须和已创建的索引保持一致
一般情况下,mongodb会自动选择索引,不需要手动hint
Stage状态分析
| stage | 描述 |
|---|---|
| COLLSCAN | 全表扫描 |
| IXSCAN | 扫描索引 |
| FETCH | 根据索引去检索指定document |
| SHARD_MERGE | 将各个分片返回数据进行merge |
| SORT | 表明在内存中进行了排序 |
| LIMIT | 使用limit限制返回数 |
| SKIP | 使用skip进行跳过 |
| IDHACK | 针对_id进行查询 |
| SHARDING_FILTER | 通过mongos对分片数据进行查询 |
| COUNT | 利用db.coll.explain().count()之类进行count运算 |
| COUNTSCAN | count不使用Index进行count时的stage返回 |
| COUNT_SCAN | count使用了Index进行count时的stage返回 |
| SUBPLA | 未使用到索引的$or查询的stage返回 |
| TEXT | 使用全文索引进行查询时候的stage返回 |
| PROJECTION | 限定返回字段时候stage的返回 |