2

这是我要查询的文档：

{
"_id":ObjectId("5062d30522dfae0e11000000"),
"id_resource" : "147",
"moment_created" : ISODate("2012-03-22T16:29:21Z"),
"moment_updated" : ISODate("2012-03-22T16:29:21Z"),
"users_involved" : [
    {
        "id_user" : "113928869",
        "state" : "answered",
        "id_folder" : "0",
        "is_deleted" : "0"
    },
    {
        "id_user" : "121624627",
        "state" : "new",
        "id_folder" : "0",
        "is_deleted" : "0" }
],
"posts" : [
    {
        "id_author" : "113928869",
        "post" : "hiohhio",
        "moment_created" : ISODate("2012-03-22T16:29:21Z")
    }
    ]
}

这就是我试图确保我的索引的方式：

db.message.ensureIndex({id_resource:1, users_involved : 1});

这是我用来查询我的收藏的查询：

db.message.find({id_resource : "143", "users_involved" : {$elemMatch : {id_user : "101226353", state : "answered"}}});

但稍后解释我得到这个输出：

{
    "clusteredType" : "ParallelSort",
    "cursor" : "BasicCursor",
    "n" : 11,
    "nChunkSkips" : 0,
    "nYields" : 8624,
    "nscanned" : 1461277,
    "nscannedAllPlans" : 1461277,
    "nscannedObjects" : 1461277,
    "nscannedObjectsAllPlans" : 1461277,
    "millisShardTotal" : 1878,
    "millisShardAvg" : 939,
    "numQueries" : 2,
    "numShards" : 2,
    "millis" : 1646

}

getIndexes 将返回：

[
    {
            "v" : 1,
            "key" : {
                    "_id" : 1
            },
            "ns" : "messaging.message",
            "name" : "_id_"
    },
    {
            "v" : 1,
            "key" : {
                    "id_resource" : 1,
                    "users_involved" : 1
            },
            "ns" : "messaging.message",
            "name" : "id_resource_1_users_involved_1"
    }

]

遗憾的是，我不明白为什么我的查询没有使用索引 id_resource_1_users_involved_1。谁能向我解释为什么不使用我的索引或者我必须如何构建索引以支持我想要使用的查询？

感谢时间和帮助

更新

对我感到羞耻，我这边的错字。所以这是查询的实际解释

{
    "clusteredType" : "ParallelSort",
    "cursor" : "BtreeCursor id_resource_1_users_involved_1",
    "n" : 5,
    "nChunkSkips" : 0,
    "nYields" : 2,
    "nscanned" : 46868,
    "nscannedAllPlans" : 93736,
    "nscannedObjects" : 46868,
    "nscannedObjectsAllPlans" : 93736,
    "millisShardTotal" : 281,
    "millisShardAvg" : 140,
    "numQueries" : 2,
    "numShards" : 2,
    "millis" : 220

}

所以查询正在使用我的索引，但它仍然很慢，nscanned 也很大，所以没有使用整个索引？我将不得不检查 nscanned 是否与资源 x 的消息量匹配

使用来自 JohnnyHK 的复合索引，它变得更快：

ensureIndex({id_resource:1, 'users_involved.id_user':1, 'users_involved.state':1});

解释

{
    "clusteredType" : "ParallelSort",
    "cursor" : "BtreeCursor id_resource_1_users_involved.id_user_1_users_involved.state_1",
    "n" : 5,
    "nChunkSkips" : 0,
    "nYields" : 0,
    "nscanned" : 7,
    "nscannedAllPlans" : 7,
    "nscannedObjects" : 7,
    "nscannedObjectsAllPlans" : 7,
    "millisShardTotal" : 0,
    "millisShardAvg" : 0,
    "numQueries" : 2,
    "numShards" : 2,
    "millis" : 1
}

所以如果我想查询 users_involved 数组，我必须为每个查询建立一个单独的索引？

还@JohnnyHK 使用提到的整个数组，如：

find({id_resource : "197", "users_involved" : {$elemMatch : {id_user : "128825371", state : "answered", id_folder:"0", is_deleted:"0"}}}).hint("id_resource_1_users_involved_1")

没有任何改善，解释：

{
    "clusteredType" : "ParallelSort",
    "cursor" : "BtreeCursor id_resource_1_users_involved_1",
    "n" : 5,
    "nChunkSkips" : 0,
    "nYields" : 1,
    "nscanned" : 46868,
    "nscannedAllPlans" : 46868,
    "nscannedObjects" : 46868,
    "nscannedObjectsAllPlans" : 46868,
    "millisShardTotal" : 222,
    "millisShardAvg" : 111,
    "numQueries" : 2,
    "numShards" : 2,
    "millis" : 174

}

或者我仍然做错了吗？

*我也从解释响应中删除了分片信息，如果此信息可能很重要，请直说

4

1 回答 1

1

因为您的复合索引包括整个users_involved数组，所以该索引只能在匹配数组的完整嵌入文档元素时使用。见这里。

我认为使用仅包含users_involved您打算搜索的字段的复合索引会更好地为您服务。所以要么：

db.message.ensureIndex({id_resource:1, 'users_involved.id_user' : 1});

或者

db.message.ensureIndex({id_resource:1, 'users_involved.id_user' : 1, 'users_involved.state' : 1});
于 2012-10-08T13:52:33.993 回答