ADR-0011: Data Quality Monitoring

Status

Accepted

Context

Data quality issues can significantly impact ML model performance. Several complex data problems needed to be addressed:

• Data consistency: New training datasets can differ significantly from previous datasets, potentially requiring changes in model architecture.
• Upstream pipeline bugs: Bugs in upstream pipelines can cause invalid values to overwrite existing valid values in an online store.
• Training/serving skew: Distribution shift between training and serving data can decrease model performance.

Feast needed a mechanism to validate data at retrieval time to catch these issues before they affect model training or serving.

Decision

Introduce a Data Quality Monitoring (DQM) module that validates datasets against user-curated rules, initially targeting historical retrieval (training dataset generation).

Design

The validation process uses a reference dataset and a profiler pattern:

1. User prepares a reference dataset (saved from a known-good historical retrieval).
2. User defines a profiler function that produces a profile (set of expectations) from a dataset.
3. Validation is performed by comparing the tested dataset against the reference profile.

Integration with Great Expectations

The initial implementation uses Great Expectations as the validation engine:

from feast.dqm.profilers.ge_profiler import ge_profiler
from great_expectations.dataset import Dataset
from great_expectations.core.expectation_suite import ExpectationSuite

@ge_profiler
def my_profiler(dataset: Dataset) -> ExpectationSuite:
    dataset.expect_column_max_to_be_between("column", 1, 2)
    dataset.expect_column_values_to_not_be_null("important_feature")
    return dataset.get_expectation_suite()

Usage

Validation is triggered during historical feature retrieval via a validation_reference parameter:

from feast import FeatureStore

store = FeatureStore(".")

job = store.get_historical_features(...)
df = job.to_df(
    validation_reference=store
        .get_saved_dataset("my_reference_dataset")
        .as_reference(profiler=my_profiler)
)

If validation fails, a ValidationFailed exception is raised with details for all expectations that didn't pass. If validation succeeds, the materialized dataset is returned normally.

Key Decisions

• Profiler-based approach: Users define their own validation rules via profiler functions rather than Feast prescribing fixed validation rules.
• Great Expectations integration: Leverages an established data validation framework rather than building custom validation logic.
• Validation at retrieval time: Validation is performed when datasets are materialized (.to_df() or .to_arrow()), not during ingestion.
• ValidationReference as a registry object: Saved datasets and their validation references are stored in the Feast registry for reuse.

Consequences

Positive

• Users can detect data quality issues before they affect model training.
• Flexible profiler pattern allows custom validation rules per use case.
• Integration with Great Expectations provides a rich set of built-in expectations.
• Reference datasets provide a baseline for detecting data drift.

Negative

• Currently limited to historical retrieval; online store write/read validation is planned but not yet implemented.
• Dependency on Great Expectations adds to the install footprint (optional via feast[ge]).
• Automatic profiling capabilities are limited; manual expectation crafting is recommended.

References

• Original RFC: Feast RFC-027: Data Quality Monitoring
• Implementation: sdk/python/feast/dqm/, sdk/python/feast/saved_dataset.py
• Documentation: Data Quality Monitoring