FeatureStore.materialize_incremental() does not initially materialize data for FeatureView with ttl=0

[chasleslr]

Expected Behavior

When executing FeatureStore.materialize_incremental() on a FeatureView that has a ttl=0 and has never yet been materialized, I would expect all historical data to be materialized since a ttl=0 indicates that features live forever according to the docs.

For an instance of FeatureView that has not explicitly defined ttl, it currently defaults to timedelta(days=0), which hints that this is indeed an expected value for ttl.

Current Behavior

Currently, the start_date for the materialization defaults to datetime.utcnow() - ttl if the feature view has not yet been materialized (i.e. FeatureView.most_recent_end_time is None). This means that start_date = datetime.utcnow() - 0s, thus start_date = datetime.utcnow(), resulting in no data being materialized.

feast/sdk/python/feast/feature_store.py

    def materialize_incremental(
        self, end_date: datetime, feature_views: Optional[List[str]] = None,
    ) -> None:
        ...
        for feature_view in feature_views_to_materialize:
            start_date = feature_view.most_recent_end_time
            if start_date is None:
                if feature_view.ttl is None:
                    raise Exception(
                        f"No start time found for feature view {feature_view.name}. materialize_incremental() requires"
                        f" either a ttl to be set or for materialize() to have been run at least once."
                    )
                >>> start_date = datetime.utcnow() - feature_view.ttl <<<
        ...

Steps to reproduce

from feast import FeatureView, FeatureStore
from datetime import datetime 

my_feature_view = FeatureView(
    name="my_feature_view",
    entities=["my_entity"],
    schema=[
        Field(name="my_feature", dtype=types.Bool)
    ],
    # ttl=timedelta(seconds=0) ; if not defined, TTL defaults to 0s
    source=sources.my_source
)

fs = FeatureStore(".")
fs.materialize_incremental(end_date=datetime.utcnow(), views=["my_feature_view"])

Specifications

• Version: 0.20.2
• Platform: macOS
• Subsystem:

Possible Solution

feast/sdk/python/feast/feature_store.py

    def materialize_incremental(
        self, end_date: datetime, feature_views: Optional[List[str]] = None,
    ) -> None:
        ...
        for feature_view in feature_views_to_materialize:
            start_date = feature_view.most_recent_end_time
            if start_date is None:
                if feature_view.ttl is None:
                    raise Exception(
                        f"No start time found for feature view {feature_view.name}. materialize_incremental() requires"
                        f" either a ttl to be set or for materialize() to have been run at least once."
                    )
                start_date = datetime.utcnow() - feature_view.ttl

                if feature_view.ttl == timedelta(days=0):
                    # what is the lower boundary for "forever" (as defined in the docs for ttl=0)?
                    # the smallest UNIX epoch timestamp could be a good candidate
                    start_date = datetime(1970,  1, 1)
        ...

[felixwang9817]

hey @chasleslr thanks for reporting this bug, and for the proposing the fix!