Supported features and syntax in Azure Cosmos DB for MongoDB 4.0 server version

Azure Cosmos DB for MongoDB 4.0 enables you to use familiar MongoDB features with enterprise-grade capabilities such as global distribution, automatic sharding, and high availability. This article describes the supported features, syntax, and benefits of using Azure Cosmos DB for MongoDB 4.0.

Protocol Support

The supported operators and any limitations or exceptions are listed here. Any client driver that understands these protocols should be able to connect to Azure Cosmos DB for MongoDB. When you create Azure Cosmos DB for MongoDB accounts, the 3.6+ versions of accounts have the endpoint in the format *.mongo.cosmos.azure.com whereas the 3.2 version of accounts has the endpoint in the format *.documents.azure.com.

Query language support

Azure Cosmos DB for MongoDB provides comprehensive support for MongoDB query language constructs. Here you can find the detailed list of currently supported operations, operators, stages, commands, and options.

Database commands

Azure Cosmos DB for MongoDB supports the following database commands:

Query and write operation commands

Transaction commands

Authentication commands

Administration commands

Diagnostics commands

Aggregation pipeline

Aggregation commands

Aggregation stages

Boolean expressions

Conversion expressions

Set expressions

Comparison expressions

Arithmetic expressions

String expressions

Text search operator

Array expressions

Variable operators

System variables

Literal operator

Date expressions

Conditional expressions

Data type operator

Accumulator expressions

Merge operator

Data types

Azure Cosmos DB for MongoDB supports documents encoded in MongoDB binary JSON (BSON) format. The 4.0 API version enhances the internal usage of this format to improve performance and reduce costs. Documents written or updated through an endpoint running 4.0+ benefit from optimization.

In an upgrade scenario to version 4.0 or later, documents created before upgrading don't immediately benefit from the enhanced performance. To take advantage of the improvements, update these documents through a write operation using the 4.0 endpoint.

16-MB document support raises the size limit for documents from 2 MB to 16 MB. This limit applies only to collections created after enabling the feature. After you enable this feature for a database account, it can't be disabled.

Enabling 16 MB can be done in the features tab in the Azure portal or programmatically by adding the EnableMongo16MBDocumentSupport capability.

We recommend enabling Server Side Retry and avoiding wildcard indexes to ensure requests with larger documents succeed. If necessary, raising your database or collection request units might also help performance.

Indexes and index properties

Indexes

Index properties

Operators

Logical operators

Element operators

Evaluation query operators

In the $regex queries, left-anchored expressions allow index search. However, using i modifier (case-insensitivity) and m modifier (multiline) causes the collection scan in all expressions.

When there's a need to include $ or |, it's best to create two (or more) regex queries. For example, given the following original query: find({x:{$regex: /^abc$/}), it has to be modified as follows:

find({x:{$regex: /^abc/, x:{$regex:/^abc$/}})

The first part uses the index to restrict the search to those documents beginning with ^abc and the second part matches the exact entries. The bar operator | acts as an "or" function - the query find({x:{$regex: /^abc |^def/}) matches the documents in which field x has values that begin with "abc" or "def". To utilize the index, break the query into two different queries joined by the $or operator: find( {$or : [{x: $regex: /^abc/}, {$regex: /^def/}] }).

Array operators

Comment operator

Projection operators

Update operators

Field update operators

Array update operators

Update modifiers

Bitwise update operator

Geospatial operators

Sort operations

When you use the findOneAndUpdate operation with API for MongoDB version 4.0, sort operations on a single field and multiple fields are supported. Sort operations on multiple fields were a limitation of previous wire protocols.

Indexing

The API for MongoDB supports various indexes to enable sorting on multiple fields, improve query performance, and enforce uniqueness.

GridFS

Azure Cosmos DB supports GridFS through any GridFS-compatible Mongo driver.

Replication

Azure Cosmos DB supports automatic, native replication at the lowest layers. This logic is extended out to achieve low-latency, global replication as well. Azure Cosmos DB doesn't support manual replication commands.

Retryable Writes

Retryable writes enable MongoDB drivers to automatically retry certain write operations if there was failure, but results in more stringent requirements for certain operations, which match MongoDB protocol requirements. With this feature enabled, update operations, including deletes, in sharded collections require the shard key to be included in the query filter or update statement.

For example, with a sharded collection, sharded on key region: To delete all the documents with the field city = "NYC", the application needs to execute the operation for all shard key (region) values if Retryable writes are enabled.

• db.coll.deleteMany({"region": "USA", "city": "NYC"}) - Succeeds with message Success
• db.coll.deleteMany({"city": "NYC"}) - Fails with error ShardKeyNotFound(61)

To enable the feature, add the EnableMongoRetryableWrites capability to your database account. This feature can also be enabled in the features tab in the Azure portal.

Sharding

Azure Cosmos DB supports automatic, server-side sharding. It manages shard creation, placement, and balancing automatically. Azure Cosmos DB doesn't support manual sharding commands, which means that you don't have to invoke commands like addShard, balancerStart, and moveChunk. You only need to specify the shard key while creating the containers or querying the data.

Sessions

Azure Cosmos DB doesn't yet support server-side sessions commands.

Time-to-live (TTL)

Azure Cosmos DB supports a time-to-live (TTL) based on the timestamp of the document. TTL can be enabled for collections from the Azure portal.

Transactions

Multi-document transactions are supported within an unsharded collection. Multi-document transactions aren't supported across collections or in sharded collections. The timeout for transactions is a fixed 5 seconds.

User and role management

Azure Cosmos DB doesn't yet support users and roles. However, Azure Cosmos DB supports Azure role-based access control and read-write and read-only passwords/keys that can be obtained through the Azure portal (Connection String page).

Write Concern

Some applications rely on a Write Concern, which specifies the number of responses required during a write operation. Due to how Azure Cosmos DB handles replication in the background all writes are automatically Quorum by default. Any write concern specified by the client code is ignored. Learn more in Using consistency levels to maximize availability and performance.