How many collections can a single Atlas cluster have?
While there is no hard limit on the number of collections in a single cluster, the performance of a cluster might degrade if it serves a large number of collections and indexes. Larger collections have a greater impact on performance.
The recommended maximum combined number of collections and indexes by Atlas cluster tier are as follows:
Cluster tier | Recommended maximum |
|---|---|
M10 | 5,000 collections and indexes |
M20 / M30 | 10,000 collections and indexes |
M40+ | 100,000 collections and indexes |
If you exceed the recommended maximum number of collections and indexes, database operations might run more slowly. Checkpoints take longer to complete, which reduces operation speed. In some cases, operations can stall if your usage exceeds your system's ulimit settings, which set limitations on the number of system resources that you can use.
Tip
To learn more about ulimit settings, see UNIX ulimit Settings for Self-Managed Deployments in the MongoDB Server Manual.
The performance impact of exceeding the recommended maximum resource number depends your collection usage. Performance impacts are more likely if you use the majority of the existing collections consistently.
Which versions of MongoDB do Atlas clusters use?
For Free and Flex clusters, Atlas manages the MongoDB version for your cluster. You can't select or change the MongoDB version manually. Atlas automatically upgrades your cluster to the latest MongoDB version after several patch releases become available.
On M10+ Atlas Core clusters, you can choose one of the following options for your cluster's MongoDB version in the Additional Settings section of the cluster form:
Select Latest Version With Auto Upgrades to use the latest MongoDB version and enable Atlas to automatically upgrade to new versions and enable new features as they become available. To learn more, see Latest Version With Auto Upgrades.
Select a specific MongoDB version from the dropdown to use that version for your cluster. You can't select a specific minor release or patch release. To see the MongoDB versions that Atlas supports, see the MongoDB Server Release Notes.
To learn more about versioning on M10+ Atlas Infinite clusters, see MongoDB Versions in Atlas.
Important
Live Migration and Mongosync are not supported on minor versions, and therefore won't work if your cluster uses Latest Version With Auto Upgrades. To migrate a cluster that is currently on a minor version, use self-guided migration tools instead.
Important
If you choose the Latest Version With Auto Upgrades release option and your cluster upgrades from a major version to a minor version, you cannot revert to a major version until the next major version release is available.
For example, if you opt in while MongoDB 8.2 is the latest release, your cluster stays on the latest minor version until MongoDB 9.0 is released. You can only revert to a major version in the window between the 9.0 release and the first minor release (9.1). If you miss that window, you cannot revert until MongoDB 10.0 is released.
As new patch releases become available, Atlas upgrades to these releases via a rolling process to maintain cluster availability. During the upgrade to the next minor release version, the cluster card in the Atlas UI Database
Deployments page might show the FCV of your cluster instead of the MongoDB version to reflect the features that are currently available on your cluster.
To learn more about how Atlas handles end of life of major MongoDB versions, see What happens to Atlas clusters using a MongoDB version nearing end of life?
When does MongoDB upgrade the database version of Free clusters?
Atlas upgrades Free clusters to the newest MongoDB version after several patch versions become available for that version. To learn more about how MongoDB versions its software, see MongoDB Versioning.
What happens to Atlas clusters using a MongoDB version nearing end of life?
Note
Unsupported MongoDB Versions in Atlas
Atlas no longer supports MongoDB 6.0 and earlier.
Atlas sends you an email notification at least six months before the MongoDB version reaches end of life. After the version cut-off date, Atlas upgrades your clusters to the default target version.
For the end-of-life policy for MongoDB versions, including when upgrades happen and what to do before the cut-off date, see MongoDB Versions and Upgrade Paths.