Time Series Collection Limitations

Unsupported Features

The following features are not supported for time series collections:

• Atlas Search

• Change streams

• Client-Side Field Level Encryption

• Database Triggers

• Schema validation rules

• reIndex

• renameCollection

Atlas Device Sync support is limited to time series collections that use Atlas Data Ingest.

Aggregation $out and $merge

You cannot use the $out or $merge aggregation pipeline stages to add data from another collection to a time series collection.

distinct Command

Due to the unique data structure of time series collections, MongoDB can't efficiently index them for distinct values. Avoid using the distinct command or db.collection.distinct() helper method on time series collections. Instead, use a $group aggregation to group documents by distinct values.

For example, to query for distinct meta.type values on documents where meta.project = 10, instead of:

db.foo.distinct("meta.type", {"meta.project": 10})

Use:

db.foo.createIndex({"meta.project":1, "meta.type":1})
db.foo.aggregate([{$match: {"meta.project": 10}},
                  {$group: {_id: "$meta.type"}}])

This works as follows:

1. Creating a compound index on meta.project and meta.type and supports the aggregation.

2. The $match stage filters for documents where meta.project = 10.

3. The $group stage uses meta.type as the group key to output one document per unique value.

Document Size

The maximum size for documents within a time series collection is 4 MB.

Updates and Deletes

Starting in MongoDB 5.1, you can perform some delete and update operations.

Delete commands must meet the following requirements:

• You can only match on metaField field values.

• Your delete command must not limit the number of documents to be deleted. Set justOne: false or use the deleteMany() method.

If a time series collection contains documents with timeField timestamps before 1970-01-01T00:00:00.000Z or after 2038-01-19T03:14:07.000Z, no documents are deleted from the collection by the TTL "time to live" feature.

For details on TTL deletes, see Expire Data from Collections by Setting TTL.

Update commands must meet the following requirements:

• You can only match on the metaField field value.

• You can only modify the metaField field value.

• Your update document can only contain update operator expressions.

• Your update command must not limit the number of documents to be updated. Set multi: true or use the updateMany() method.

• Your update command must not set upsert: true.

In MongoDB 5.0, time series collections only support insert operations and read queries. Updates and manual delete operations result in an error.

To automatically delete old data, set up automatic removal (TTL).

To remove all documents from a collection, use the drop() method to drop the collection.

Time Series Secondary Indexes

There is improved support for secondary indexes in MongoDB 6.0.

Capped Collections

You cannot create a time series collection as a capped collection.

Modification of Collection Type

You can only set the collection type when you create a collection:

• An existing collection cannot be converted into a time series collection.

• A time series collection cannot be converted into a different collection type.

To move data from an existing collection to a time series collection, migrate data into a time series collection.

Modification of timeField and metaField

You can only set a collection's timeField and metaField parameters when you create the collection. You cannot modify these parameters later.

Modification of granularity

After you set the granularity, you can only increase it one level at a time. The granularity can change from "seconds" to "minutes" or from "minutes" to "hours". Other changes are not allowed.

To change the granularity from "seconds" to "hours", first increase the granularity to "minutes" and then to "hours".

Sharding

Starting in MongoDB 5.1 (and 5.0.6), you can create sharded time series collections.

In versions earlier than MongoDB 5.0.6, you cannot shard time series collections.

Transactions

You cannot write to time series collections in transactions.

View Limitations

Time series collections are writable non-materialized views. Limitations for views apply to time series collections.

• You cannot create a view from a time series bucket collection namespace (namely, a collection prefixed with system.buckets).

Snapshot Isolation

Read operations on time series collections with read concern "snapshot" guarantee snapshot isolation only in the absence of concurrent drop or rename operations on collections in the read operation. Re-creating a time series collection on the same namespace with different granularity setting does not yield full snapshot isolation.