更新：我创建了一个票证：https://jira.mongodb.org/browse/SERVER-48777
请参见以下示例。为什么第二查询执行文档查找？
db.createCollection('inventory')
db.getCollection('inventory').insertMany([
{ type: 'food', color: 'yellow', name: 'banana' },
{ type: 'food', color: 'red', name: 'cherry' },
{ type: 'car', color: 'yellow', name: 'taxi' }
])
db.getCollection('inventory').createIndex({ type: 1, name: 1 }, { name: 'byType' })
db.getCollection('inventory').createIndex({ name: 1 }, { name: 'onlyRed', partialFilterExpression: { color: 'red' } })
// find cherry by type -> totalDocsExamined = 0 (as expected)
db.getCollection('inventory').find({ type: 'food', name: /c/ }, { name: 1, _id: 0 }).explain('executionStats').executionStats.totalDocsExamined
// find cherry by color -> totalDocsExamined = 1 :-(
db.getCollection('inventory').find({ color: 'red', name: /c/ }, { name: 1, _id: 0 }).explain('executionStats').executionStats.totalDocsExamined
以上示例的索引为：
db.getCollection('inventory').getIndexes()
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
},
{
"v" : 2,
"key" : {
"type" : 1.0,
"name" : 1.0
},
"name" : "byType"
},
{
"v" : 2,
"key" : {
"name" : 1.0
},
"name" : "onlyRed",
"partialFilterExpression" : {
"color" : "red"
}
}
]
以下所有版本均显示此行为：4.2.1、4.2.7、4.4.0-rc9
我在Covered Queries和Partial Indexes的文档中找不到任何内容，为什么不应该支持它。
query1的解释：
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "demo.inventory",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"type" : {
"$eq" : "food"
}
},
{
"name" : {
"$regex" : "c"
}
}
]
},
"winningPlan" : {
"stage" : "PROJECTION_COVERED",
"transformBy" : {
"name" : 1.0,
"_id" : 0.0
},
"inputStage" : {
"stage" : "IXSCAN",
"filter" : {
"name" : {
"$regex" : "c"
}
},
"keyPattern" : {
"type" : 1.0,
"name" : 1.0
},
"indexName" : "byType",
"isMultiKey" : false,
"multiKeyPaths" : {
"type" : [],
"name" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"type" : [
"[\"food\", \"food\"]"
],
"name" : [
"[\"\", {})",
"[/c/, /c/]"
]
}
}
},
"rejectedPlans" : []
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 0,
"totalKeysExamined" : 2,
"totalDocsExamined" : 0,
"executionStages" : {
"stage" : "PROJECTION_COVERED",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 1,
"needTime" : 1,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"transformBy" : {
"name" : 1.0,
"_id" : 0.0
},
"inputStage" : {
"stage" : "IXSCAN",
"filter" : {
"name" : {
"$regex" : "c"
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 3,
"advanced" : 1,
"needTime" : 1,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"keyPattern" : {
"type" : 1.0,
"name" : 1.0
},
"indexName" : "byType",
"isMultiKey" : false,
"multiKeyPaths" : {
"type" : [],
"name" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"type" : [
"[\"food\", \"food\"]"
],
"name" : [
"[\"\", {})",
"[/c/, /c/]"
]
},
"keysExamined" : 2,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
},
"serverInfo" : {
"host" : "mongo",
"port" : 27017,
"version" : "4.4.0-rc9",
"gitVersion" : "bea79f76addfe4b754c8696db029c5b3c762041c"
},
"ok" : 1.0,
"$clusterTime" : {
"clusterTime" : Timestamp(1591984674, 1),
"signature" : {
"hash" : { "$binary" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=", "$type" : "00" },
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1591984674, 1)
}
query2的解释（使用部分索引）：
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "demo.inventory",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"color" : {
"$eq" : "red"
}
},
{
"name" : {
"$regex" : "c"
}
}
]
},
"winningPlan" : {
"stage" : "PROJECTION_SIMPLE",
"transformBy" : {
"name" : 1.0,
"_id" : 0.0
},
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"color" : {
"$eq" : "red"
}
},
"inputStage" : {
"stage" : "IXSCAN",
"filter" : {
"name" : {
"$regex" : "c"
}
},
"keyPattern" : {
"name" : 1.0
},
"indexName" : "onlyRed",
"isMultiKey" : false,
"multiKeyPaths" : {
"name" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : true,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"\", {})",
"[/c/, /c/]"
]
}
}
}
},
"rejectedPlans" : []
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 0,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"executionStages" : {
"stage" : "PROJECTION_SIMPLE",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"transformBy" : {
"name" : 1.0,
"_id" : 0.0
},
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"color" : {
"$eq" : "red"
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"docsExamined" : 1,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"filter" : {
"name" : {
"$regex" : "c"
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"keyPattern" : {
"name" : 1.0
},
"indexName" : "onlyRed",
"isMultiKey" : false,
"multiKeyPaths" : {
"name" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : true,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"name" : [
"[\"\", {})",
"[/c/, /c/]"
]
},
"keysExamined" : 1,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
}
},
"serverInfo" : {
"host" : "mongo",
"port" : 27017,
"version" : "4.4.0-rc9",
"gitVersion" : "bea79f76addfe4b754c8696db029c5b3c762041c"
},
"ok" : 1.0,
"$clusterTime" : {
"clusterTime" : Timestamp(1591984064, 1),
"signature" : {
"hash" : { "$binary" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=", "$type" : "00" },
"keyId" : NumberLong(0)
}
},
"operationTime" : Timestamp(1591984064, 1)
}
答案 0 :(得分：0)
事实证明，这是一个已知错误，已经在此处进行跟踪：https://jira.mongodb.org/browse/SERVER-26580
此问题的创建日期为2016年10月11日。：-（
答案 1 :(得分：0)
虽然您知道在MongoDB Jira中跟踪的这些类型的索引存在局限性，但是对此有一个简单的解决方法-将部分索引表达式中的字段添加到索引定义中作为键。这将允许选择仅索引计划。