In-Memory Storage Engine


The in-memory storage engine is currently in beta. Do not use in production.

Starting in MongoDB Enterprise 3.2, an in-memory storage engine is available in the 64-bit builds for beta-testing purposes. Other than some metadata and diagnoistic data, the in-memory storage engine does not maintain any on-disk data. By avoiding disk I/O, the in-memory storage engine allows for more predictable latency of database operations.

Specify In-Memory Storage Engine

To select the in-memory storage engine, specify:

  • inMemory for the --storageEngine option, or the storage.engine setting if using a configuration file.
  • --dbpath, or storage.dbPath if using a configuration file. Although the in-memory storage engine does not write data to the filesystem, it maintains in the --dbpath small metadata files and diagnostic data as well temporary files for building large indexes.

For example, from the command line:

mongod --storageEngine inMemory --dbpath <path>

Or, if using the YAML configuration file format:

   engine: inMemory
   dbPath: <path>

See inMemory Options for configuration options specific to this storage engine.


The in-memory storage engine does not persist data after process shutdown.


The in-memory storage engine uses document-level concurrency control for write operations. As a result, multiple clients can modify different documents of a collection at the same time.


The in-memory storage engine is non-persistent and does not write data to a persistent storage. As such, the concept of journal or waiting for data to become durable does not apply to the in-memory storage engine.

Write operations that specify a write concern journaled are acknowledged immediately. When an mongod instance shuts down, either as result of the shutdown command or due to a system error, recovery of in-memory data is impossible.

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