Add documentation.

Signed-off-by: Casey Clements <casey.clements@mongodb.com>
feast-dev · ntkathole · Mar 10, 2026 · Jan 20, 2026 · Jan 20, 2026 · Feb 12, 2026
commit 7f5a192a8ce60f7a677c738829fad75953b51ed6
@@ -131,6 +131,7 @@
   * [ScyllaDB](reference/online-stores/scylladb.md)
   * [SingleStore](reference/online-stores/singlestore.md)
   * [Milvus](reference/online-stores/milvus.md)
+  * [MongoDB](reference/online-stores/mongodb.md)
 * [Registries](reference/registries/README.md)
   * [Local](reference/registries/local.md)
   * [S3](reference/registries/s3.md)

@@ -50,6 +50,10 @@ Please see [Online Store](../../getting-started/components/online-store.md) for
 [mysql.md](mysql.md)
 {% endcontent-ref %}
 
+{% content-ref url="mongodb.md" %}
+[mongodb.md](mongodb.md)
+{% endcontent-ref %}
+
 {% content-ref url="hazelcast.md" %}
 [hazelcast.md](hazelcast.md)
 {% endcontent-ref %}

@@ -0,0 +1,181 @@
+# MongoDB online store (Alpha)
+
+## Description
+
+The [MongoDB](https://www.mongodb.com/) online store provides support for materializing feature values into MongoDB for serving online features.
+
+{% hint style="warning" %}
+The MongoDB online store is currently in **alpha development**. Some functionality may be unstable, and breaking changes may occur in future releases.
+{% endhint %}
+
+## Features
+
+* Supports both synchronous and asynchronous operations for high-performance feature retrieval
+* Native async support uses PyMongo's `AsyncMongoClient` (no Motor dependency required)
+* Flexible connection options supporting MongoDB Atlas, self-hosted MongoDB, and MongoDB replica sets
+* Automatic index creation for optimized query performance
+* Entity key collocation for efficient feature retrieval
+
+## Getting started
+
+In order to use this online store, you'll need to install the MongoDB extra (along with the dependency needed for the offline store of choice):
+
+```bash
+pip install 'feast[mongodb]'
+```
+
+You can get started by using any of the other templates (e.g. `feast init -t gcp` or `feast init -t snowflake` or `feast init -t aws`), and then swapping in MongoDB as the online store as seen below in the examples.
+
+## Examples
+
+### Basic configuration with MongoDB Atlas
+
+{% code title="feature_store.yaml" %}
+```yaml
+project: my_feature_repo
+registry: data/registry.db
+provider: local
+online_store:
+  type: mongodb
+  connection_string: "mongodb+srv://username:password@cluster.mongodb.net/"
+  database_name: feast_online_store
+```
+{% endcode %}
+
+### Self-hosted MongoDB with authentication
+
+{% code title="feature_store.yaml" %}
+```yaml
+project: my_feature_repo
+registry: data/registry.db
+provider: local
+online_store:
+  type: mongodb
+  connection_string: "mongodb://username:password@localhost:27017/"
+  database_name: feast_online_store
+  collection_suffix: features
+```
+{% endcode %}
+
+### MongoDB replica set configuration
+
+{% code title="feature_store.yaml" %}
+```yaml
+project: my_feature_repo
+registry: data/registry.db
+provider: local
+online_store:
+  type: mongodb
+  connection_string: "mongodb://host1:27017,host2:27017,host3:27017/?replicaSet=myReplicaSet"
+  database_name: feast_online_store
+  client_kwargs:
+    retryWrites: true
+    w: majority
+```
+{% endcode %}
+
+### Advanced configuration with custom client options
+
+{% code title="feature_store.yaml" %}
+```yaml
+project: my_feature_repo
+registry: data/registry.db
+provider: local
+online_store:
+  type: mongodb
+  connection_string: "mongodb+srv://cluster.mongodb.net/"
+  database_name: feast_online_store
+  collection_suffix: features
+  client_kwargs:
+    maxPoolSize: 50
+    minPoolSize: 10
+    serverSelectionTimeoutMS: 5000
+    connectTimeoutMS: 10000
+```
+{% endcode %}
+
+The full set of configuration options is available in [MongoDBOnlineStoreConfig](https://rtd.feast.dev/en/latest/#feast.infra.online_stores.contrib.mongodb_online_store.mongodb.MongoDBOnlineStoreConfig).
+
+## Data Model
+
+The MongoDB online store uses a **single collection per project** with entity key collocation. Features from multiple feature views for the same entity are stored together in a single document.
+
+### Example Document Schema
+
+The example shows a single entity. It contains 3 features from 2 feature views: "rating" and "trips_last7d" from Feature
+View "driver_stats", and "surge_multiplier" from "pricing" view. 
+Each feature view has its own event timestamp. 
+The "created_timestamp" marks when the entity was materialized.
+
+```javascript
+{
+  "_id": "<serialized_entity_key>",  // Binary entity key (bytes)
+  "features": {
+    "driver_stats": {
+      "rating": 4.91,
+      "trips_last_7d": 132
+    },
+    "pricing": {
+      "surge_multiplier": 1.2
+    }
+  },
+  "event_timestamps": {
+    "driver_stats": ISODate("2026-01-20T12:00:00Z"),
+    "pricing": ISODate("2026-01-21T08:30:00Z")
+  },
+  "created_timestamp": ISODate("2026-01-21T12:00:05Z")
+}
+```
+
+### Key Design Decisions
+
+* **`_id` field**: Uses the serialized entity key (bytes) as the primary key for efficient lookups
+* **Nested features**: Features are organized by feature view name, allowing multiple feature views per entity
+* **Event timestamps**: Stored per feature view to track when each feature set was last updated
+* **Created timestamp**: Global timestamp for the entire document
+
+### Indexes
+
+The online store automatically creates the following index:
+* Primary key index on `_id` (automatic in MongoDB), set to the serialized entity key.
+
+No additional indexes are required for the online store operations.
+
+## Async Support
+
+The MongoDB online store provides native async support using PyMongo 4.13+'s stable `AsyncMongoClient`. This enables:
+
+* **High concurrency**: Handle thousands of concurrent feature requests without thread pool limitations
+* **True async I/O**: Non-blocking operations for better performance in async applications
+* **10-20x performance improvement**: For concurrent workloads compared to sequential sync operations
+
+Both sync and async methods are fully supported:
+* `online_read` / `online_read_async`
+* `online_write_batch` / `online_write_batch_async`
+
+## Functionality Matrix
+
+The set of functionality supported by online stores is described in detail [here](overview.md#functionality).
+Below is a matrix indicating which functionality is supported by the MongoDB online store.
+
+|                                                           | MongoDB |
+| :-------------------------------------------------------- | :------ |
+| write feature values to the online store                  | yes     |
+| read feature values from the online store                 | yes     |
+| update infrastructure (e.g. tables) in the online store   | yes     |
+| teardown infrastructure (e.g. tables) in the online store | yes     |
+| generate a plan of infrastructure changes                 | no      |
+| support for on-demand transforms                          | yes     |
+| readable by Python SDK                                    | yes     |
+| readable by Java                                          | no      |
+| readable by Go                                            | no      |
+| support for entityless feature views                      | yes     |
+| support for concurrent writing to the same key            | yes     |
+| support for ttl (time to live) at retrieval               | no      |
+| support for deleting expired data                         | no      |
+| collocated by feature view                                | no      |
+| collocated by feature service                             | no      |
+| collocated by entity key                                  | yes     |
+
+To compare this set of functionality against other online stores, please see the full [functionality matrix](overview.md#functionality-matrix).
+
@@ -0,0 +1,29 @@
+feast.infra.online\_stores.mongodb\_online\_store package
+=================================================================
+
+Submodules
+----------
+
+feast.infra.online\_stores.mongodb\_online\_store.mongodb module
+------------------------------------------------------------------------
+
+.. automodule:: feast.infra.online_stores.mongodb_online_store.mongodb
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+feast.infra.online\_stores.mongodb\_online\_store.mongodb\_repo\_configuration module
+---------------------------------------------------------------------------------------------
+
+.. automodule:: feast.infra.online_stores.mongodb_online_store.mongodb_repo_configuration
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
+Module contents
+---------------
+
+.. automodule:: feast.infra.online_stores.mongodb_online_store
+   :members:
+   :undoc-members:
+   :show-inheritance:
@@ -13,6 +13,7 @@ Subpackages
    feast.infra.online_stores.hazelcast_online_store
    feast.infra.online_stores.hbase_online_store
    feast.infra.online_stores.milvus_online_store
+   feast.infra.online_stores.mongodb_online_store
    feast.infra.online_stores.mysql_online_store
    feast.infra.online_stores.postgres_online_store
    feast.infra.online_stores.qdrant_online_store