Amazon DocumentDB compatibility with MongoDB

Increased storage limit to 128 TiB for all instance-based Amazon DocumentDB clusters and shard-based elastic clusters.

Introduced Amazon DocumentDB 5.0 Engine Version 3.0.775)

The backup built-in role now supports serverStatus. Action - Developers and applications with backup role can collect statistics about the state of the Amazon DocumentDB cluster.

The SecondaryDelaySecs field replaces slaveDelay in replSetGetConfig output.

The hello command replaces isMaster - hello returns a document that describes the role of a Amazon DocumentDB cluster.

Amazon DocumentDB 5.0 now supports index scans with the $elemMatch operator in the first nesting level. Index scans are supported when the query only filter has one level of the $elemMatch filter but are not supported if a nested $elemMatch query is included.

For example, in Amazon DocumentDB 5.0, if you include the $elemMatch operator in the nested level, it will not return a value as it does in Amazon DocumentDB 4.0:

db.foo.insert(
[
    {a: {b: 5}},
    {a: {b: [5]}},
    {a: {b: [3, 7]}},
    {a: [{b: 5}]},
    {a: [{b: 3}, {b: 7}]},
    {a: [{b: [5]}]},
    {a: [{b: [3, 7]}]},
    {a: [[{b: 5}]]},
    {a: [[{b: 3}, {b: 7}]]},
    {a: [[{b: [5]}]]},
    {a: [[{b: [3, 7]}]]}
]);

// DocumentDB 5.0
> db.foo.find({a: {$elemMatch: {b: {$elemMatch: {$lt: 6, $gt: 4}}}}}, {_id: 0})
{ "a" : [ { "b" : [ 5 ] } ] }

// DocumentDB 4.0
> db.foo.find({a: {$elemMatch: {b: {$elemMatch: {$lt: 6, $gt: 4}}}}}, {_id: 0})
{ "a" : [ { "b" : [ 5 ] } ] }
{ "a" : [ [ { "b" : [ 5 ] } ] ] }

The "$" projection in Amazon DocumentDB 4.0 returns all documents with all fields. With Amazon DocumentDB 5.0, the find command with a "$" projection returns documents that match the query parameter containing only the field that matched the "$" projection.

In Amazon DocumentDB 5.0, the find commands with $regex and $options query parameters return an error: "Cannot set options in both $regex and $options".

With Amazon DocumentDB 5.0, $indexOfCP now returns "-1" when:

In Amazon DocumentDB 4.0, $indexOfCP returns "0" when the start position is a number greater than end or the byte length of the string.

With Amazon DocumentDB 5.0, projection operations in _id fields, for example {"_id.nestedField" : 1}, return documents that only include the projected field. Whereas in Amazon DocumentDB 4.0, nested field projection commands do not filter out any document.

ACID Transactions: Amazon DocumentDB now supports the ability to perform transactions across multiple documents, statements, collections, and databases. Transactions simplify application development by enabling you to perform atomic, consistent, isolated, and durable (ACID) operations across one or more documents within an Amazon DocumentDB cluster. For more information, see Transactions in Amazon DocumentDB.

Change streams: You now have the ability to open a change stream at the cluster level (client.watch() or mongo.watch()) and the database (db.watch()), you can specify a startAtOperationTime to open a change stream cursor, and lastly you can now extend your change stream retention period to 7 days (previously 24 hours). For more information, see Using change streams with Amazon DocumentDB.

AWS Database Migration Service (AWS DMS): You can now use AWS DMS to migrate your MongoDB 4.0 workloads to Amazon DocumentDB. AWS DMS now supports a MongoDB 4.0 source, Amazon DocumentDB 4.0 target, and an Amazon DocumentDB 3.6 source for performing upgrades between Amazon DocumentDB 3.6 and 4.0. For more information, see AWS DMS Documentation.

Performance and indexing: You can now utilize an index with $lookup, find queries with a projection that contain one field or one field and the _id field can be served direct from the index and without needing to read from the collection (covered query), the ability to hint() with findAndModify, performance optimizations for $addToSet, and improvements to reduce overall index sizes. For more information, see Release notes.

Operators: Amazon DocumentDB 4.0 now supports a number of new aggregation operators: $ifNull, $replaceRoot, $setIsSubset, $setIntersection, $setUnion, $setEquals. You can see all the MongoDB APIs, Operations, and Data Types that we support at Supported MongoDB APIs, operations, and data types in Amazon DocumentDB.

Role based access control (RBAC): With both ListCollection and ListDatabase commands you can now optionally use the authorizedCollections and authorizedDatabases parameters to allow users to list the collections and databases that they have permission to access without requiring the listCollections and listDatabase roles, respectively. You also have the ability to kill your own cursors without requiring the KillCursor role.

Projection for nested documents: Amazon DocumentDB 3.6 considers the first field in a nested document when applying a projection. However, Amazon DocumentDB 4.0 will parse subdocuments and apply the projection to each sub document as well. For example: if the projection is "a.b.c": 1, then the behavior in both versions is identical. However, if the projection is {a:{b:{c:1}}} then Amazon DocumentDB 3.6 will only apply the projection to 'a' and not 'b' or 'c'.

Behavior for minKey, maxKey: In Amazon DocumentDB 4.0, the behavior for {x:{$gt:MaxKey}} returns nothing, and for {x:{$lt:MaxKey}} returns everything.

Document comparison differences: Comparing numerical values of different types (double, int, long) in subdocuments (e.g., b in {"_id" :1, "a" :{"b":1}}) now provides a consistent output across numerical data types and for each level of a document.

Lookup with empty key in path: When a collection contains a document with empty key inside the array (e.g. {"x" : [ { "" : 10 }, { "b" : 20 } ]}), and when the key used in the query ends in an empty string (e.g. x.), then Amazon DocumentDB will return that document since it traverses all the documents in the array whereas MongoDB will not return that document.

$setOnInsert along with $ in the path: The field operator $setOnInsert will not work in combination with $ in the path in Amazon DocumentDB, which is also consistent with MongoDB 4.0.