$indexStats (aggregation)

Definition定义

$indexStats

Returns statistics regarding the use of each index for the collection. 返回有关集合中每个索引使用情况的统计信息。If running with access control, the user must have privileges that include indexStats action.如果使用访问控制运行，用户必须具有包括indexStats操作的权限。

The $indexStats stage takes an empty document and has the following syntax:$indexStats阶段取用两个空文档，并且语法如下：

{ $indexStats: { } }

For each index, the return document includes the following fields:对于每个索引，返回文档包括以下字段：

Output Field输出场	Description描述
name	Index name.索引名。
key	Index key specification.索引键规范。 See also: spec.另见：规范。
host	The hostname and port of the mongod process.mongod进程的主机名和端口。
accesses	Statistics on the index use:指数使用统计： ops is the number of operations that used the index.是使用索引的操作数。 since is the time from which MongoDB gathered the statistics.是MongoDB集合统计数据的时间。
shard	The name of the shard associated with the host与host关联的分片的名称 Only available for a sharded cluster.仅适用于分片群集。 New in version 4.2.4.在版本4.2.4中新增。
spec	The full specfication document for the index, which includes the index key specification document.索引的完整规范文档，包括索引键规范文档。 The index option hidden, available starting in MongoDB 4.4, is only included if the value is true.索引选项hidden从MongoDB 4.4开始可用，仅在值为true时才包含。 New in version 4.2.4.在版本4.2.4中新增。
building	Indicates if the index is currently being built.指示当前是否正在生成索引。 Only available if true.仅当为true时可用。 New in version 4.2.4.在版本4.2.4中新增。

Statistics for an index will be reset on mongod restart or index drop and recreation.在mongod重新启动或索引删除和重新创建时，将重置索引的统计信息。

Behavior行为

Example示例

For example, a collection orders contains the following documents:例如，集合orders包含以下文档：

{ "_id" : 1, "item" : "abc", "price" : 12, "quantity" : 2, "type": "apparel" }
{ "_id" : 2, "item" : "jkl", "price" : 20, "quantity" : 1, "type": "electronics" }
{ "_id" : 3, "item" : "abc", "price" : 10, "quantity" : 5, "type": "apparel" }

Create the following two indexes on the collection:在集合上创建以下两个索引：

db.orders.createIndex( { item: 1, quantity: 1 } )
db.orders.createIndex( { type: 1, item: 1 } )

Run some queries against the collection:对集合运行一些查询：

db.orders.find( { type: "apparel"} )
db.orders.find( { item: "abc" } ).sort( { quantity: 1 } )

To view statistics on the index use on the orders collection, run the following aggregation operation:要查看orders集合上索引使用的统计信息，请运行以下聚合操作：

db.orders.aggregate( [ { $indexStats: { } } ] )

The operation returns a document that contains usage statistics for each index:该操作返回一个文档，其中包含每个索引的使用统计信息：

{
   "name" : "item_1_quantity_1",
   "key" : { "item" : 1, "quantity" : 1 },
   "host" : "examplehost.local:27018",
   "accesses" : {
      "ops" : NumberLong(1),
      "since" : ISODate("2020-02-10T21:11:23.059Z")
   },
   "shard" : "shardA",
      // Available starting in MongoDB 4.2.4 if run on sharded cluster
   "spec" : {
               // Available starting in MongoDB 4.2.4
      "v" : 2,
      "key" : { "item" : 1, "quantity" : 1 },
      "name" : "item_1_quantity_1"
   }
}
{
   "name" : "item_1_price_1",
   "key" : { "item" : 1, "price" : 1 },
   "host" : "examplehost.local:27018",
   "accesses" : {
      "ops" : NumberLong(1),
      "since" : ISODate("2020-02-10T21:11:23.233Z")
   },
   "shard" : "shardA",
      // Available starting in MongoDB 4.2.4 if run on sharded cluster
   "spec" : {
               // Available starting in MongoDB 4.2.4
      "v" : 2,
      "key" : { "item" : 1, "price" : 1 },
      "name" : "item_1_price_1"
   }
}
{
   "name" : "item_1",
   "key" : { "item" : 1 },
   "host" : "examplehost.local:27018",
   "accesses" : {
      "ops" : NumberLong(0),
      "since" : ISODate("2020-02-10T21:11:22.947Z")
   },
   "shard" : "shardA",
      // Available starting in MongoDB 4.2.4 if run on sharded cluster
   "spec" : {
               // Available starting in MongoDB 4.2.4
      "v" : 2,
      "key" : { "item" : 1 },
      "name" : "item_1"
   }
}
{
   "name" : "_id_",
   "key" : { "_id" : 1 },
   "host" : "examplehost.local:27018",
   "accesses" : {
      "ops" : NumberLong(0),
      "since" : ISODate("2020-02-10T21:11:18.298Z")
   },
   "shard" : "shardA",
      // Available starting in MongoDB 4.2.4 if run on sharded cluster
   "spec" : {
               // Available starting in MongoDB 4.2.4
      "v" : 2,
      "key" : { "_id" : 1 },
      "name" : "_id_"
   }
}