RFC00001: Snowflake Feature Pull Connector for BharatMLStack

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RFC00001: Snowflake Feature Pull Connector for BharatMLStack

Metadata

• Author: Adarsha Das
• Date Created: 2025-07-05
• Status: Draft
• Target Release: v1.1.0
• Discussion Channel: #connectors-snowflake

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1. Summary

This proposal introduces native support for Snowflake as an offline feature store and describes an end-to-end pipeline that ports those features into BharatMLStack's online feature store so they can be served for real-time inference. The connector retrieves features from Snowflake using the snowflake.ml.feature_store API, applies the transformation/deduplication logic in data_helpers.py, then relies on spark_feature_push_client to serialize the resulting Spark DataFrame into Protobuf and push it—via Kafka or another configured sink—into the online store. The aim is to provide a single, frictionless path from Snowflake to online serving with zero intermediate exports.

2. Motivation

1. Industry Adoption – Snowflake is the de-facto cloud data warehouse for many ML teams.
2. Unified Governance – Keeping features in Snowflake allows teams to reuse established data contracts, lineage, and RBAC.
3. Performance & Scale – Snowflake's automatic scaling matches BharatMLStack's design philosophy of elastic cost.
4. Developer Ergonomics – The snowflake.ml.feature_store SDK abstracts low-level SQL and improves developer productivity.

Without this connector, users have to export data to object storage before ingesting it, introducing latency and operational overhead.

3. Goals

• Add SNOWFLAKE_TABLE as a new source_type value consumed by read_from_source().
• Use the snowflake.ml.feature_store.FeatureStore abstraction for reading data, not raw JDBC.
• Support predicate-pushdown on a configurable partition column (default: ingestion_timestamp).
• Preserve existing semantics: the helper must return a Spark DataFrame deduplicated on entity keys.
• Provide clear configuration & credential management guidelines.
• Seamlessly push the transformed Snowflake features to BharatMLStack's online feature store through spark_feature_push_client, enabling immediate consumption at inference time.

4. Non-Goals

• Online serving from Snowflake (future work).
• Bi-directional sync or writing features back into Snowflake.
• Support for Snowflake external tables or stages (out of scope for first version).

5. Detailed Design

5.1 Data Pull Flow

1. Session Creation – A snowpark.Session is established using env-vars or a passed-in config map.
2. Feature Store Bind – Instantiate FeatureStore(session).
3. Table Selection – Retrieve the maximum value of the partition column via the Feature Store API.
4. Data Retrieval – Load the filtered rows into a Spark DataFrame through feature_store.read().to_spark().
5. Schema Alignment – Column names are normalized and optionally renamed according to feature_mapping.

5.2 Data Push Flow

1. Null Handling & Default Filling – Invoke fill_na_features_with_default_values to replace missing values based on feature metadata.
2. Proto Generation – Use OnlineFeatureStorePyClient.generate_df_with_protobuf_messages (from spark_feature_push_client) to convert rows into Protobuf messages.
3. Batching & Kafka Write – Call write_protobuf_df_to_kafka, optionally in batches, to stream messages to the online feature-store ingress topic.
4. Audit Sink (Optional) – If features_write_to_cloud_storage is true, persist the transformed DataFrame to the configured cloud path for replay or debugging.
5. Online Availability – Once consumed by BharatMLStack's ingestion service, features become queryable for real-time inference within SLA (p95 < X s).

5.3 API Touch-Points

Function	Change	Rationale
read_from_source()	Add elif source_type == "SNOWFLAKE_TABLE" branch to perform steps in 5.1	Aligns with existing connector pattern
src_type_to_partition_col_map	Append "SNOWFLAKE_TABLE": "ingestion_timestamp"	Ensures incremental loads

5.4 Configuration

Parameter	Description	Example
SNOWFLAKE_ACCOUNT	Snowflake account identifier	xy12345.us-east-1
SNOWFLAKE_USER	Login user	ml_readonly
SNOWFLAKE_PASSWORD	Password or OAuth token	****
SNOWFLAKE_WAREHOUSE	Virtual warehouse used for queries	ML_WH
SNOWFLAKE_DATABASE	Database containing feature tables	FEATURE_DB
SNOWFLAKE_SCHEMA	Default schema	PUBLIC

Credentials are loaded by helper utilities and injected into the Snowpark session. Users may override through function arguments for multi-account scenarios.

5.5 Error Handling & Observability

• Retry Logic: Exponential backoff for transient Snowflake errors (XYZ-0001, XYZ-0002).
• Metrics:
  • snowflake.connector.latency_ms
  • snowflake.connector.rows_read
  • snowflake.connector.bytes_scanned
• Logging: Obfuscate sensitive parameters before logging connection strings.

6. Test Plan

1. Unit Tests – Mock snowflake.ml.feature_store to simulate data fetches.
2. Integration Tests – Use Snowflake's TPCH_SF1 sample to validate partition filtering, column renaming, null-handling, Protobuf generation, and successful push to the online feature store.
3. Schema Drift Tests – Verify connector surface errors when expected columns are missing or types change.

7. Rollout Strategy

Phase	Description
Alpha	Flag-guarded release for internal users. Collect feedback.
Beta	Publicly documented. Backwards compatibility guaranteed.
GA	Remove feature flag. Add SLA monitoring.

8. Alternatives Considered

• Spark JDBC Connector – Simpler, but lacks feature-store metadata awareness and type mapping.
• Materializing Views to Parquet – Adds latency and duplication of storage.

9. Risks & Mitigations

Risk	Impact	Mitigation
Snowflake API instability	Ingest failures	Pin to major version; add compatibility tests
Credential leakage	Security breach	Use secrets manager integration; no plaintext logs
Large data pulls	Cost overruns	Enforce partition filters; sample row counts during CI

10. Success Metrics

• 100% schema parity with Snowflake source tables.

11. Future Work

• Automatic statistics push to BharatML observability dashboard.

12. References

• Snowflake ML Feature Store Documentation (2024-04) — "snowflake.ml.feature_store".

RFC PR