$indexStats (aggregation)¶

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Definition
Behavior
Example

Definition¶

$indexStats¶

New in version 3.2.

Returns statistics regarding the use of each index for the collection. If running with access control, the user must have privileges that include indexStats action.

The $indexStats stage takes an empty document and has the following syntax:

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{ $indexStats: { } }

The return document includes the following fields:

Output Field	Description
`name`	Index name.
`key`	Index key specification.
`host`	The hostname and port of the `mongod` process.
`accesses`	Statistics on the index use: `ops` is the number of operations that used the index. `since` is the time from which MongoDB gathered the statistics.

Statistics for an index will be reset on mongod restart or index drop and recreation.

Note

Prior to version 3.2.3, the ops field value did not include $match or mapReduce operations that use indexes.

Behavior¶

The statistics reported by the accesses field only includes index access driven by user requests. It does not include internal operations like deletion via TTL Indexes or chunk split and migration operations.

$indexStats must be the first stage in an aggregation pipeline.

Example¶

For example, a collection orders contains the following documents:

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{ "_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:

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

Run some queries against the collection:

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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:

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

The operation returns a document that contains usage statistics for each index:

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{
   "name" : "item_1_quantity_1",
   "key" : {
      "item" : 1,
      "quantity" : 1
   },
   "host" : "examplehost.local:27017",
   "accesses" : {
      "ops" : NumberLong(1),
      "since" : ISODate("2015-10-02T14:31:53.685Z")
   }
}
{
   "name" : "_id_",
   "key" : {
      "_id" : 1
   },
   "host" : "examplehost.local:27017",
   "accesses" : {
      "ops" : NumberLong(0),
      "since" : ISODate("2015-10-02T14:31:32.479Z")
   }
}
{
   "name" : "type_1_item_1",
   "key" : {
      "type" : 1,
      "item" : 1
   },
   "host" : "examplehost.local:27017",
   "accesses" : {
      "ops" : NumberLong(1),
      "since" : ISODate("2015-10-02T14:31:58.321Z")
   }
}

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