Archive Data

Cluster Requirements

Online Archive in Atlas is available only on M10 and greater clusters.

Required Permissions

To create or delete an Online Archive, you must have one of these roles:

• Project Data Access Admin role

• Project Cluster Manager role

• Project Owner role

How Atlas Archives Data

To archive data:

1. For each archive, Atlas runs a query in the archive's namespace to identify the documents that match the criteria for archiving. Atlas refers to this query on a particular archive's namespace as a job.

   By default, Atlas runs the job every five minutes. If the size of documents to archive doesn't meet the threshold, Atlas expands the job interval by five minutes, up to a maximum of four hours. If the job interval reaches the maximum or if the size of documents to archive reaches the threshold, Atlas runs the job again and resets the job interval to five minutes. The threshold is 2GB per job.

   Atlas might initiate the job from any node in the cluster. However, since the job might need to perform delete operations, it always connects to the primary member.

   If you specify a time window when you want to run the job, Atlas runs the job continuously during that time window as long as there is at least 5 MiB of data to archive. To learn more, see Limitations. If a running job doesn't complete during the time window, Atlas continues to run the job until it completes. If all archiving jobs reach the maximum threshold for either the size or number of documents to archive during three consecutive archive windows, we recommend that you increase the frequency.

   Atlas runs an index sufficiency query to determine the efficiency of the archival process. If the number of documents scanned to the number of documents returned is 10 or more, the query result triggers an Index Sufficiency Warning. This warning indicates that you have insufficient indexes for an efficient archival process. For date-based archives, you must index the date field. For custom criteria that use an expression, Atlas might first convert a value before it evaluates it against the query.

2. For documents that match the archival criteria, Atlas:

   1. Writes to up to a maximum of 10,000 partitions per data archiving job.

   2. Writes up to 2GB of document data to partitions on the cloud object storage for each unique combination of query field values except dates, which are grouped during each run to reduce the number of partitions.

   3. Writes each subsequent quantity of document data (up to 2 GB) with each query run.

Online Archive runs on your Atlas cluster and uses the same underlying resources, such as IOPS. The default limit of 2GB per job prevents the operation from using too many resources. If your cluster is currently satisfying workloads at the edge of its resource limits, you could push it past its capacity by activating Online Archive. Ensure that your Atlas cluster has excess resources before activating Online Archive.

If you activate Online Archive, you can select one of the following regions to store your archived data.

When you archive data, Atlas first copies the data to the cloud object storage and then deletes the data from your Atlas cluster. During archival, for a brief period of time, you might see duplicate documents on your Atlas cluster and the Online Archive. But after the archival and when your Online Archive state is idle, the already archived documents won't be present in your Atlas cluster.

WiredTiger doesn't release the storage blocks of the deleted data back to the OS for performance reasons. However, Atlas eventually automatically reuses these storage blocks for new data. This helps the Atlas cluster to avoid fragmentation. To learn more, see How do I reclaim disk space in WiredTiger?.

Your Online Archive is read-only. Atlas doesn't update archived data. You can configure deletion of archived data after a certain period of time. To purge archived data, configure the Deletion Age Limit setting for your Online Archive when you create or modify the Online Archive. Atlas doesn't sync your Online Archive with the Atlas cluster to maintain consistency after the data is archived.

Atlas provides a unified endpoint. You can use it to query all databases and collections on your live cluster and archived data using the same database and collection name that you use in your Atlas cluster. You can't use the unified endpoint over a Network Peering Connection, but you can set up a private endpoint or use a standard internet connection over TLS.

Limitations

Online Archive doesn't support the following:

• Writing to the Online Archive.

• Configuring or administering the Online Archive federated database instance through the Atlas console, Atlas Data Federation CLI, or Atlas Data Federation API.

• Archiving a capped collection.

• Archiving data below the size of 5 MiB after 7 days. To learn more, see Limitations.

• GridFS.

Viewing the Online Archive

To view your federated database instance for the Online Archive:

Querying the Online Archive

To query your Online Archive data, use the connection string through the Online Archive or federated database instance Connect button to connect to the federated database instance.

You can also query your Online Archive data with SQL. To learn more, see Query with Atlas SQL.

Managing Query Limits for Online Archive

You can configure limits on the amount of data that is processed for your queries against archived data to control the data processing costs for your Online Archive. When the amount of processed data reaches any applicable configured limit, Atlas won't execute any new queries and returns an error to the client application that a limit has been reached. You can also optionally configure query termination to terminate queries that exceed the limit. To learn more, see Manage Atlas Data Federation Query Limits.

Editing Online Archives

Once Atlas creates the Online Archive, you can't change the archiving criteria from Date Match to Custom Filter, or vice versa.

Deleting Online Archives

If you delete all the Online Archives, Atlas deletes the federated database instances. After deleting all the Online Archives, if you create an Online Archive with the same settings as a deleted Online Archive, Atlas creates a new federated database instance for the new Online Archive.