我试图重现索引交集指令的第一个示例( http://docs.mongodb.org/manual/core/index-intersection/ )，但面临一个问题:mongo 不使用两个索引
我的步骤:
- 下载 mongo (3.0.3) 并安装
- 运行 mongod:mongod.exe --dbpath d:\data(文件夹为空)
- 运行 mongo:mongo.exe
添加索引:
db.orders.ensureIndex({ qty: 1 }) db.orders.ensureIndex({ item: 1 }) db.orders.getIndexes() [{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.orders" }, { "v" : 1, "key" : { "qty" : 1 }, "name" : "qty_1", "ns" : "test.orders" }, { "v" : 1, "key" : { "item" : 1 }, "name" : "item_1", "ns" : "test.orders" }]检查查询说明:
db.orders.find( { item: "abc123", qty: { $gt: 15 } } ).explain() { "queryPlanner" : { "plannerVersion" : 1, "namespace" : "test.orders", "indexFilterSet" : false, "parsedQuery" : { "$and" : [ { "item" : { "$eq" : "abc123" } }, { "qty" : { "$gt" : 15 } } ] }, "winningPlan" : { "stage" : "KEEP_MUTATIONS", "inputStage" : { "stage" : "FETCH", "filter" : { "qty" : { "$gt" : 15 } }, "inputStage" : { "stage" : "IXSCAN", "keyPattern" : { "item" : 1 }, "indexName" : "item_1", "isMultiKey" : false, "direction" : "forward", "indexBounds" : { "item" : [ "[\"abc123\", \"abc123\"]" ] } } } }, "rejectedPlans" : [ { "stage" : "KEEP_MUTATIONS", "inputStage" : { "stage" : "FETCH", "filter" : { "item" : { "$eq" : "abc123" } }, "inputStage" : { "stage" : "IXSCAN", "keyPattern" : { "qty" : 1 }, "indexName" : "qty_1", "isMultiKey" : false, "direction" : "forward", "indexBounds" : { "qty" : [ "(15.0, 1.#INF]" ] } } } } ] }, "serverInfo" : { "host" : "localhost", "port" : 27017, "version" : "3.0.3", "gitVersion" : "b40106b36eecd1b4407eb1ad1af6bc60593c6105" }, "ok" : 1 }
如您所见，winingPlan 仅包含 item_1 索引。有一个包含 qty_1 索引的rejectedPlans。但没有包含索引交集的计划。 我知道选择特定索引有很多条件。但就我而言，mongo 甚至没有计划它!
有人可以帮助我吗？
最佳答案
SERVER-3071 JIRA issue中有一些关于索引选择的详细信息。但我不能说所有内容是否仍然与 3.0 相关。无论如何:
MongoDB 3.0.2似乎不考虑范围查询的索引交互。但它会针对点间隔:
> db.orders.find( { item: {$eq : "abc123"}, qty: { $eq: 15 } } ).explain()
...
{
"stage" : "FETCH",
"inputStage" : {
"stage" : "KEEP_MUTATIONS",
"inputStage" : {
"stage" : "AND_SORTED",
"inputStages" : [
{
"stage" : "IXSCAN",
"keyPattern" : {
"qty" : 1
},
"indexName" : "qty_1",
"isMultiKey" : false,
"direction" : "forward",
"indexBounds" : {
"qty" : [
"[15.0, 15.0]"
]
}
},
{
"stage" : "IXSCAN",
"keyPattern" : {
"item" : 1
},
"indexName" : "item_1",
"isMultiKey" : false,
"direction" : "forward",
"indexBounds" : {
"item" : [
"[\"abc123\", \"abc123\"]"
]
}
}
]
}
关于mongodb - 为什么 MongoDB 不使用索引交集？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30626726/