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dbStats (database command)

Definition

dbStats: The dbStats command returns storage statistics for a given database.

Compatibility

This command is available in deployments hosted in the following environments:

MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

Important

This command has limited support in M0 and Flex clusters. For more information, see Unsupported Commands.

MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB

Syntax

The command has the following syntax:

db.runCommand(
   {
     dbStats: 1,
     scale: <number>,
     freeStorage: 0
   }
)

Command Fields

The command takes the following fields:

Fields	Description
`dbStats`	1
scale	Optional. The scale factor for the various size data. The `scale` defaults to 1 to return size data in bytes. To display kilobytes rather than bytes, specify a `scale` value of `1024`. If you specify a non-integer scale factor, MongoDB uses the integer part of the specified factor. For example, if you specify a scale factor of `1023.999`, MongoDB uses `1023` as the scale factor. Starting in version 4.2, the output includes the `scaleFactor` used to scale the size values.
freeStorage	Optional. To return details on free space allocated to collections, set `freeStorage` to 1. If the instance has a large number of collections or indexes, obtaining free space usage data may cause processing delays. To gather `dbStats` information without free space details, either set `freeStorage` to 0 or do not include the field.

In mongosh, the db.stats() function provides a wrapper around dbStats.

Behavior

The time required to run the command depends on the total size of the database. Because the command must touch all data files, the command may take several seconds to run.

Accuracy after Unexpected Shutdown

After an unclean shutdown of a mongod using the Wired Tiger storage engine, count and size statistics reported by dbStats may be inaccurate.

The amount of drift depends on the number of insert, update, or delete operations performed between the last checkpoint and the unclean shutdown. Checkpoints usually occur every 60 seconds. However, mongod instances running with non-default --syncdelay settings may have more or less frequent checkpoints.

Run validate on each collection on the mongod to restore statistics after an unclean shutdown.

After an unclean shutdown:

validate updates the count statistic in the collStats output with the latest value.
Other statistics like the number of documents inserted or removed in the collStats output are estimates.

Replica Set Member State Restriction

To run on a replica set member, dbStats operations require the member to be in PRIMARY or SECONDARY state. If the member is in another state, such as STARTUP2, the operation errors.

Output

dbStats.db: Name of the database.

dbStats.collections: Number of collections in the database.

dbStats.views: Number of views in the database.

dbStats.objects: Number of objects (specifically, documents) in the database across all collections.

dbStats.avgObjSize: Average size of each document in bytes. This is the dataSize divided by the number of documents. The scale argument does not affect the avgObjSize value.

dbStats.dataSize

Total size of the uncompressed data held in the database. The dataSize decreases when you remove documents.

For databases using the WiredTiger storage engine, dataSize may be larger than storageSize if compression is enabled. The dataSize decreases when documents shrink.

dbStats.storageSize

Sum of the disk space allocated to all collections in the database for document storage, including free space.

The storageSize does not decrease as you remove or shrink documents. This value may be smaller than dataSize for databases using the WiredTiger storage engine with compression enabled.

storageSize does not include space allocated to indexes. See indexSize for the total index size.

dbStats.freeStorageSize

Sum of the free space allocated to all collections in the database for document storage. Free database storage space is allocated to the collection but does not contain data.

freeStorageSize does not include free space allocated to indexes. See indexFreeStorageSize for the total free index size.

To include this value in the dbStats output, set freeStorage to 1.

Updated in version 5.3.0, 5.2.1, and 5.0.6

dbStats.indexes: Total number of indexes across all collections in the database.

dbStats.indexSize: Sum of the disk space allocated to all indexes in the database, including free index space.
Note
In clustered collections with only a default index on the _ìd field (no secondary indexes), the index size appears as zero because the collection does not require a separate index file.

dbStats.indexFreeStorageSize

Sum of the free disk space allocated to all indexes in the database. Free database storage space is allocated to the index but does not contain data.

indexFreeStorageSize does not include free space allocated to document storage. See freeStorageSize for the total free document storage size.

indexFreeStorageSize does not include in-progress index builds.

To include this value in the dbStats output, set freeStorage to 1.

Updated in version 7.0, 6.3.2, 6.0.7, 5.3.0, 5.2.1, 5.0.19, and 5.0.6

dbStats.totalSize: Sum of the disk space allocated for both documents and indexes in all collections in the database. Includes used and free storage space. This is the sum of storageSize and indexSize.

dbStats.totalFreeStorageSize

Sum of the free storage space allocated for both documents and indexes in all collections in the database. This is the sum of freeStorageSize and indexFreeStorageSize.

To include this value in the dbStats output, set freeStorage to 1.

Updated in version 5.3.0, 5.2.1, and 5.0.6.

dbStats.scaleFactor

scale value used by the command.

If you specified a non-integer scale factor, MongoDB uses the integer part of the specified factor. For example, if you specify a scale factor of 1023.999, MongoDB uses 1023 as the scale factor.

dbStats.fsUsedSize: Total size of all disk space in use on the filesystem where MongoDB stores data.
Tip
--dbpath

dbStats.fsTotalSize: Total size of all disk capacity on the filesystem where MongoDB stores data.

Examples

The following examples demonstrate dbStats usage.

Limit Data Returned

To limit the data returned to a single field, append the field name to the dbStats command. This example returns the indexSize value:

db.runCommand( { dbStats: 1 } ).indexSize

View Free Space Allocated to Collections

To view free storage usage, set freeStorage to 1.

db.runCommand( { dbStats: 1, scale: 1024, freeStorage: 1 } )

Example output:

{
  db: 'test',
  collections: 2,
  views: 0,
  objects: 1689,
  avgObjSize: 52.56542332741267,
  dataSize: 86.7021484375,
  storageSize: 100,
  freeStorageSize: 32,
  indexes: 2,
  indexSize: 116,
  indexFreeStorageSize: 36,
  totalSize: 216,
  totalFreeStorageSize: 68,
  scaleFactor: 1024,
  fsUsedSize: 60155820,
  fsTotalSize: 61255492,
  ok: 1,
  '$clusterTime': {
    clusterTime: Timestamp({ t: 1646085664, i: 1 }),
    signature: {
      hash: Binary(Buffer.from("0000000000000000000000000000000000000000", "hex"), 0),
      keyId: Long("0")
    }
  },
  operationTime: Timestamp({ t: 1646085664, i: 1 })
}

The freeStorage field enables the collection and display of the highlighted metrics.

The scale field sets the displayed values to kilobytes.

Back

dbHash

explain

Definition

Compatibility

Important

Syntax

Command Fields

Behavior

Accuracy after Unexpected Shutdown

Replica Set Member State Restriction

Output

Note

Tip

Examples

Limit Data Returned

View Free Space Allocated to Collections