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Diagnostic Commands

dbStats

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  • Definition
  • Syntax
  • Command Fields
  • Behavior
  • Output
  • Examples

Definition

dbStats

The dbStats command returns storage statistics for a given database.

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
1

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.

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

Starting in MongoDB 4.4, 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.

In previous versions, the operations also run when the member is in STARTUP2. The operations wait until the member transitioned to RECOVERING.

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 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 space allocated to all indexes in the database, including free index space.

dbStats.indexFreeStorageSize

Sum of the free 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.

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.totalSize

Sum of the 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.

New in version 4.4.

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.

New in version 4.2.

dbStats.fsUsedSize

Total size of all disk space in use on the filesystem where MongoDB stores data.

Tip

See also:

--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.

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