我有以下命令：
db.mycol.find({sourceId:ObjectId("596bac5a6f473e1a042bFFFF"),myFlag:false}).count()
花了很多时间。
所以我决定添加一个索引{ "sourceId" : -1, "myFlag" : -1 }
MongoDB仍然保持同一时间。
当我在find命令上运行explain()时，我注意到mongoDB仍然使用我的旧索引。
db.mycol.find({sourceId:ObjectId("596bac5a6f473e1a042bFFFF"),myFlag:false}).explain(true)
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "mydb.mycol",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"sourceId" : {
"$eq" : ObjectId("596bac5a6f473e1a042bFFFF")
}
},
{
"myFlag" : {
"$eq" : false
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"sourceId" : 1
},
"indexName" : "sourceId_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
]
}
}
},
"rejectedPlans" : [
{
"stage" : "FETCH",
"filter" : {
"sourceId" : {
"$eq" : ObjectId("596bac5a6f473e1a042bFFFF")
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"myFlag" : -1
},
"indexName" : "myFlag_-1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"myFlag" : [
"[false, false]"
]
}
}
},
{
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"sourceId" : -1,
"timestamp" : -1
},
"indexName" : "sourceId_-1_timestamp_-1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
],
"timestamp" : [
"[MaxKey, MinKey]"
]
}
}
},
{
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"sourceId" : -1,
"timestamp" : 1
},
"indexName" : "sourceId_-1_timestamp_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
],
"timestamp" : [
"[MinKey, MaxKey]"
]
}
}
},
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"sourceId" : -1,
"myFlag" : -1
},
"indexName" : "sourceId_-1_myFlag_-1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
],
"myFlag" : [
"[false, false]"
]
}
}
}
]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 2074,
"executionTimeMillis" : 33936,
"totalKeysExamined" : 2074,
"totalDocsExamined" : 2074,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"nReturned" : 2074,
"executionTimeMillisEstimate" : 31710,
"works" : 2075,
"advanced" : 2074,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 2074,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 2074,
"executionTimeMillisEstimate" : 0,
"works" : 2075,
"advanced" : 2074,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"sourceId" : 1
},
"indexName" : "sourceId_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
]
},
"keysExamined" : 2074,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
},
"allPlansExecution" : [
{
"nReturned" : 0,
"executionTimeMillisEstimate" : 1630,
"totalKeysExamined" : 101,
"totalDocsExamined" : 101,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"sourceId" : {
"$eq" : ObjectId("596bac5a6f473e1a042bFFFF")
}
},
"nReturned" : 0,
"executionTimeMillisEstimate" : 1630,
"works" : 101,
"advanced" : 0,
"needTime" : 101,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 101,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"myFlag" : -1
},
"indexName" : "myFlag_-1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"myFlag" : [
"[false, false]"
]
},
"keysExamined" : 101,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
{
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"totalKeysExamined" : 101,
"totalDocsExamined" : 101,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 101,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"sourceId" : -1,
"timestamp" : -1
},
"indexName" : "sourceId_-1_timestamp_-1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
],
"timestamp" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 101,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
{
"nReturned" : 101,
"executionTimeMillisEstimate" : 10,
"totalKeysExamined" : 101,
"totalDocsExamined" : 101,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"nReturned" : 101,
"executionTimeMillisEstimate" : 10,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 101,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"sourceId" : -1,
"timestamp" : 1
},
"indexName" : "sourceId_-1_timestamp_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
],
"timestamp" : [
"[MinKey, MaxKey]"
]
},
"keysExamined" : 101,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
{
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"totalKeysExamined" : 101,
"totalDocsExamined" : 101,
"executionStages" : {
"stage" : "FETCH",
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 101,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 1554,
"restoreState" : 1554,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"sourceId" : -1,
"myFlag" : -1
},
"indexName" : "sourceId_-1_myFlag_-1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
],
"myFlag" : [
"[false, false]"
]
},
"keysExamined" : 101,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
},
{
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"totalKeysExamined" : 101,
"totalDocsExamined" : 101,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"myFlag" : {
"$eq" : false
}
},
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 88,
"restoreState" : 88,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 101,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 101,
"executionTimeMillisEstimate" : 0,
"works" : 101,
"advanced" : 101,
"needTime" : 0,
"needYield" : 0,
"saveState" : 88,
"restoreState" : 88,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"sourceId" : 1
},
"indexName" : "sourceId_1",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"sourceId" : [
"[ObjectId('596bac5a6f473e1a042bFFFF'), ObjectId('596bac5a6f473e1a042bFFFF')]"
]
},
"keysExamined" : 101,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
]
},
"serverInfo" : {
"host" : "gdm3d",
"port" : 27017,
"version" : "3.2.15",
"gitVersion" : "e11e3c1b9c9ce3f7b4a79493e16f5e4504e01140"
},
"ok" : 1
}
出于某种原因，它拒绝使用sourceId_-1_myFlag_-1的计划并与sourceId_1一起使用，然后按文档过滤myFlag。
当我强制它使用索引时，它立即返回结果！
db.mycol.find({sourceId:ObjectId("596bac5a6f473e1a042bFFFF"),myFlag:false}).hint("sourceId_-1_myFlag_-1").count()
我认为mongoDB定期运行所有计划并检查哪一个更快，然后再使用那个计划。
我甚至尝试重新启动mongodb，清除查询计划缓存，重新启动计算机。对于一些数据量非常少的sourceId，它确实自动使用了正确的索引（我检查了索引用法），然后再次使用旧索引。
我不想强迫它使用索引。我如何确保它自动执行此操作？
更新
一段时间后，它开始使用正确的一个。至少是indexStats所说的。
但是，该命令仍然需要时间，当我给它hint时，它会立即给出输出。