dbStats¶

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Definition
Behavior
Output

Definition¶

dbStats¶

The dbStats command returns storage statistics for a given database. The command takes the following syntax:

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

scale is optional and defaults to 1.

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

Behavior¶

The scale argument allows you to specify how to scale byte values. For example, a scale value of 1024 will display the results in kilobytes rather than in bytes:

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

Note

Scaling rounds values to whole numbers.

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 the correct statistics after an unclean shutdown.

Output¶

dbStats.db¶: Contains the name of the database.

dbStats.collections¶: Contains a count of the number of collections in that database.

dbStats.objects¶: Contains a count of the number of objects (i.e. documents) in the database across all collections.

dbStats.avgObjSize¶: The 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¶

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

For databases using the MMAPv1 storage engine, dataSize includes preallocated space and the padding factor. The dataSize does not decrease when documents shrink.

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¶: The total amount of space allocated to collections in this database for document storage. 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.

dbStats.numExtents¶: Contains a count of the number of extents in the database across all collections.

dbStats.indexes¶: Contains a count of the total number of indexes across all collections in the database.

dbStats.indexSize¶: The total size of all indexes created on this database.

dbStats.fileSize¶

The total size of the data files that hold the database. This value includes preallocated space and the padding factor. The value of fileSize only reflects the size of the data files for the database and not the namespace file.

Only present when using the mmapv1 storage engine.

dbStats.nsSizeMB¶

The total size of the namespace files (i.e. that end with .ns) for this database. You cannot change the size of the namespace file after creating a database, but you can change the default size for all new namespace files with the nsSize runtime option.

Only present when using the mmapv1 storage engine.