$indexStats (aggregation)

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Definition

Behavior
Example

Definition

$indexStats

Returns statistics regarding the use of each index for the collection. If running with access control, authenticate as a user with at least the clusterMonitor role.

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

{ $indexStats: { } }

For each index, the return document includes the following fields:

Output Field	Description
`name`	Index name.
key	Index key specification. See also: spec.
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.
shard	The name of the shard associated with the host Only available for a sharded cluster.
spec	The full specification document for the index, which includes the index key and index properties. The index option `hidden` is only included if the value is `true`.
building	Indicates if the index is currently being built. Only available if `true`.

Behavior

Accesses Field

The statistics reported by the accesses field only apply to the node where the query is being run and only include index access driven by user requests. It does not include internal operations like deletion via TTL Indexes or chunk split and migration operations.

Restrictions

$indexStats must be the first stage in an aggregation pipeline.
$indexStats is not allowed in transactions.

Index Statistics Reset Considerations

Statistics for an index reset on mongod restart or index drop and recreation.
Modification of an existing index (see collMod command) resets the statistics for that index.

Example

For example, a collection orders contains the following documents:

db.orders.insertMany( [
   { _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:

db.orders.createIndex( { item: 1, quantity: 1 } )
db.orders.createIndex( { type: 1, item: 1 } )
db.orders.createIndex(
   { price: 1 },
   { partialFilterExpression: { type: "apparel" } }
)

Run some queries against the collection:

db.orders.find( { type: "apparel"} )
db.orders.find( { item: "abc" } ).sort( { quantity: 1 } )
db.orders.find( { price: { $gt: 10 } } )

To view statistics on the index use on the orders collection, run the following aggregation operation:

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

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

[
   {
      name: 'type_1_item_1',
      key: { type: 1, item: 1 },
      host: 'examplehost.local:27018',
      accesses: { ops: Long("1"), since: ISODate("2024-05-02T15:07:21.420Z") },
      shard: "shardA",
      spec: { v: 2, key: { type: 1, item: 1 }, name: 'type_1_item_1' }
   },
   {
      name: 'item_1_quantity_1',
      key: { item: 1, quantity: 1 },
      host: 'examplehost.local:27018',
      accesses: { ops: Long("1"), since: ISODate("2024-05-02T15:07:21.254Z") },
      shard: "shardA",
      spec: { v: 2, key: { item: 1, quantity: 1 }, name: 'item_1_quantity_1' }
   },
   {
      name: '_id_',
      key: { _id: 1 },
      host: 'examplehost.local:27018',
      accesses: { ops: Long("0"), since: ISODate("2024-05-02T15:07:13.274Z") },
      shard: "shardA",
      spec: { v: 2, key: { _id: 1 }, name: '_id_' }
   },
   {
      name: 'price_1',
      key: { price: 1 },
      host: 'examplehost.local:27018',
      accesses: { ops: Long("0"), since: ISODate("2024-05-02T15:07:54.847Z") },
      shard: "shardA",
      spec: {
         v: 2,
         key: { price: 1 },
         name: 'price_1',
         partialFilterExpression: { type: 'apparel' }
      }
   }
]

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