MongoDB offline store (contrib)

Description

The MongoDB offline store provides support for reading MongoDBSource.

• Uses a single shared collection with a compound index for all FeatureViews, distinguished by a feature_view discriminator field.
• Entity dataframes can be provided as a Pandas dataframe. The offline store converts entity identifiers into serialized entity keys for efficient lookup against the collection.

Getting started

In order to use this offline store, you'll need to run pip install 'feast[mongodb]'.

Example

{% code title="feature_store.yaml" %}

project: my_project
registry: data/registry.db
provider: local
offline_store:
  type: feast.infra.offline_stores.contrib.mongodb_offline_store.mongodb.MongoDBOfflineStore
  connection_string: "mongodb+srv://user:[email protected]"  # pragma: allowlist secret
  database: feast
  collection: feature_history
online_store:
  type: mongodb
  connection_string: "mongodb+srv://user:[email protected]"  # pragma: allowlist secret
  database_name: feast_online_store
  collection_suffix: latest
  client_kwargs: {}

{% endcode %}

The full set of configuration options is available in MongoDBOfflineStoreConfig.

Data Model

The offline store uses a single shared collection (by default feature_history) that stores append-only historical feature rows for all feature views. Each document represents one observation of one entity for one FeatureView at a specific event timestamp:

{
  "entity_id": "Binary(...)",
  "feature_view": "driver_stats",
  "event_timestamp": "ISODate(2024-01-15T12:00:00Z)",
  "created_at": "ISODate(2024-01-15T12:01:00Z)",
  "features": {
    "conv_rate": 0.72,
    "acc_rate": 0.91,
    "avg_daily_trips": 14
  }
}

Key properties:

• Append-only: Historical data is treated as immutable; corrections are written as new rows with newer created_at timestamps rather than in-place updates.
• Time-series friendly: event_timestamp represents when the feature value was observed; created_at is used as a tie-breaker when multiple observations share the same event timestamp.
• Feature grouping by FeatureView: feature_view identifies which FeatureView the row belongs to, so a single collection can host multiple FVs.

A single compound index supports all major query patterns:

(entity_id ASC, feature_view ASC, event_timestamp DESC, created_at DESC)

This index enables efficient range scans over entities and feature views, while ensuring that the most recent observation per (entity_id, feature_view) is seen first during aggregation. The index is created lazily on first use and cached per connection string.

Key Optimizations

• Scoring vs. training paths: When each entity appears only once in entity_df (scoring/inference — one feature lookup per entity), server-side $group $first efficiently returns the single latest value per entity. When the same entity appears at multiple timestamps (training — building a dataset with many historical snapshots per entity), the store retrieves all candidate rows and uses pd.merge_asof to select the correct point-in-time value for each request timestamp.
• Two-level chunking: CHUNK_SIZE (50,000 rows) controls the size of intermediate DataFrames in memory; MONGO_BATCH_SIZE (10,000 entity IDs) limits the query size sent to MongoDB.

Functionality Matrix

The set of functionality supported by offline stores is described in detail here. Below is a matrix indicating which functionality is supported by the MongoDB offline store.

Below is a matrix indicating which functionality is supported by MongoDBRetrievalJob.

To compare this set of functionality against other offline stores, please see the full functionality matrix.