java - MongoDB 不使用多键索引

Question

我有一个 MongoDB 版本 3.0.3 集合，其中包含具有 2 个字段的文档:

• 数字长 ID
• 由 60 个 double 字组成的数组。

我在数组上构建了一个多键索引，并使用 getIndexInfo() 方法确认该索引存在并且是多键。但是，当我查询数组中 2 个特定字段范围的交集时，Mongo 不使用此索引，尽管集合中有 1,000,000 个文档。我可以从 explain() 方法的输出中看到这一点。更奇怪的是，当我通过 hint 指定使用索引时，Mongo 会遍历所有 1,000,000 个文档和 60,000,000 个索引条目，我在 explain() 的输出中看到了这一点。

我使用以下代码构建查询:

BasicDBObject q2 = new BasicDBObject("array.0",new BasicDBObject("$lt",1000.0));
BasicDBObject q1 = new BasicDBObject("array.1",new BasicDBObject("$gte",800.0));
BasicDBObject q_and = new BasicDBObject("$and",Arrays.asList(q1,q2));
dbo = collection.find(q_and).explain();

有什么想法吗？

预先感谢您的帮助。

回复解释输出的请求:

在不指定提示的情况下，解释输出如下:

{ "queryPlanner" : 
{ "plannerVersion" : 1 , "namespace" : "local.TestArrays" , "indexFilterSet" : false , "parsedQuery" : 
{ "$and" : [ 
{ "array.0" : 
{ "$lt" : 1000.0
}
} , 
{ "array.1" : 
{ "$gte" : 800.0
}
}]
} , "winningPlan" : 
{ "stage" : "COLLSCAN" , "filter" : 
{ "$and" : [ 
{ "array.0" : 
{ "$lt" : 1000.0
}
} , 
{ "array.1" : 
{ "$gte" : 800.0
}
}]
} , "direction" : "forward"
} , "rejectedPlans" : [ ]
} , "executionStats" : 
{ "executionSuccess" : true , "nReturned" : 2 , "executionTimeMillis" : 2248 , "totalKeysExamined" : 0 , "totalDocsExamined" : 1000000 , "executionStages" : 
{ "stage" : "COLLSCAN" , "filter" : 
{ "$and" : [ 
{ "array.0" : 
{ "$lt" : 1000.0
}
} , 
{ "array.1" : 
{ "$gte" : 800.0
}
}]
} , "nReturned" : 2 , "executionTimeMillisEstimate" : 2190 , "works" : 1000002 , "advanced" : 2 , "needTime" : 999999 , "needFetch" : 0 , "saveState" : 7812 , "restoreState" : 7812 , "isEOF" : 1 , "invalidates" : 0 , "direction" : "forward" , "docsExamined" : 1000000
} , "allPlansExecution" : [ ]
} , "serverInfo" : 
{ "host" : "NYDEVWS0005052" , "port" : 27017 , "version" : "3.0.3" , "gitVersion" : "b40106b36eecd1b4407eb1ad1af6bc60593c6105"
}
}

指定要与以下代码一起使用的索引时:

collection.find(q_and).hint("array_1").explain();

解释输出如下:

{ "queryPlanner" : 
{ "plannerVersion" : 1 , "namespace" : "local.TestArrays" , "indexFilterSet" : false , "parsedQuery" : 
{ "$and" : [ 
{ "array.0" : 
{ "$lt" : 1000.0
}
} , 
{ "array.1" : 
{ "$gte" : 800.0
}
}]
} , "winningPlan" : 
{ "stage" : "KEEP_MUTATIONS" , "inputStage" : 
{ "stage" : "FETCH" , "filter" : 
{ "$and" : [ 
{ "array.0" : 
{ "$lt" : 1000.0
}
} , 
{ "array.1" : 
{ "$gte" : 800.0
}
}]
} , "inputStage" : 
{ "stage" : "IXSCAN" , "keyPattern" : 
{ "array" : 1
} , "indexName" : "array_1" , "isMultiKey" : true , "direction" : "forward" , "indexBounds" : 
{ "array" : [ "[MinKey, MaxKey]"]
}
}
}
} , "rejectedPlans" : [ ]
} , "executionStats" : 
{ "executionSuccess" : true , "nReturned" : 2 , "executionTimeMillis" : 61401 , "totalKeysExamined" : 60000000 , "totalDocsExamined" : 1000000 , "executionStages" : 
{ "stage" : "KEEP_MUTATIONS" , "nReturned" : 2 , "executionTimeMillisEstimate" : 56570 , "works" : 60001744 , "advanced" : 2 , "needTime" : 59999998 , "needFetch" : 1743 , "saveState" : 470130 , "restoreState" : 470130 , "isEOF" : 1 , "invalidates" : 0 , "inputStage" : 
{ "stage" : "FETCH" , "filter" : 
{ "$and" : [ 
{ "array.0" : 
{ "$lt" : 1000.0
}
} , 
{ "array.1" : 
{ "$gte" : 800.0
}
}]
} , "nReturned" : 2 , "executionTimeMillisEstimate" : 55620 , "works" : 60001744 , "advanced" : 2 , "needTime" : 59999998 , "needFetch" : 1743 , "saveState" : 470130 , "restoreState" : 470130 , "isEOF" : 1 , "invalidates" : 0 , "docsExamined" : 1000000 , "alreadyHasObj" : 0 , "inputStage" : 
{ "stage" : "IXSCAN" , "nReturned" : 1000000 , "executionTimeMillisEstimate" : 50820 , "works" : 60000000 , "advanced" : 1000000 , "needTime" : 59000000 , "needFetch" : 0 , "saveState" : 470130 , "restoreState" : 470130 , "isEOF" : 1 , "invalidates" : 0 , "keyPattern" : 
{ "array" : 1
} , "indexName" : "array_1" , "isMultiKey" : true , "direction" : "forward" , "indexBounds" : 
{ "array" : [ "[MinKey, MaxKey]"]
} , "keysExamined" : 60000000 , "dupsTested" : 60000000 , "dupsDropped" : 59000000 , "seenInvalidated" : 0 , "matchTested" : 0
}
}
} , "allPlansExecution" : [ ]
} , "serverInfo" : 
{ "host" : "NYDEVWS0005052" , "port" : 27017 , "version" : "3.0.3" , "gitVersion" : "b40106b36eecd1b4407eb1ad1af6bc60593c6105"
}
}

Answer 1

我误解了多键索引的含义。我认为为数组中的每个位置创建了一个单独的索引。然而，在进一步阅读后，我发现为数组创建了单个索引，并且文档的所有条目都输入到该单个索引中，而不保留数组位置。我采纳了 n9code 的建议，创建了单独的字段并在每个字段上创建了索引。这按预期工作。