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

• GraphQL API

• Atlas Device Sync (Atlas Device Sync is supported if the time series collections are asymmetrically synchronized. For details, see Enable Atlas Device Sync.)

• reIndex

• Schema validation rules

Constraints

The maximum size of a measurement document is 4 MB.

Aggregation $out and $merge

You can't use aggregation pipeline stages $out and $merge to output or merge into to time series collections from another 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 5.0.5, you can perform some delete and update operations.

Delete commands must meet the following requirements:

• The query may only match on metaField field values.

• The delete command may not limit the number of documents to be deleted. You must use a delete command with justOne: false or the deleteMany() method.

Update commands must meet the following requirements:

• The query may only match on metaField field values.

• The update command may only modify the metaField field value.

• The update must be performed with an update document that contains only update operator expressions.

• The update command may not limit the number of documents to be updated. You must use an update command with multi: true or the updateMany() method.

• The update command may not set upsert: true.

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.

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.

Secondary Indexes

You can add secondary indexes on the fields specified as the timeField and the metaField. If the field value for the metaField field is a document, you can also create secondary indexes on fields inside that document.

The metaField doesn't support the following index types:

• 2d

• 2dsphere

• text

Secondary indexes don't support the following index properties:

• TTL

• Unique

• Partial

Capped Collections

A time series collection can't be created as a capped collection.

Modification of Collection Type

A collection's type can only be set when creating the collection:

• An existing collection can't be converted into a time series collection.

• A time series collection can't 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 creating the collection. After creation these parameters can't be modified.

Modification of granularity

Once the granularity is set it can only be increased by one level at a time. From "seconds" to "minutes" or from "minutes" to "hours". Other changes are not allowed. If you need to change the granularity from "seconds" to "hours", first increase the granularity to "minutes" and then to "hours".

Sharding

Starting in MongoDB 5.0.6, sharded time series collections are supported. When using sharded time series collections, you cannot modify the granularity of a sharded time series collection.

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

Transactions

You can't write to time series collections in transactions.

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.