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Version: 0.5

Batch Feature View

A Batch Feature View defines transformations against one or more Batch Sources, which are data sources (e.g. S3, Hive, Redshift, Snowflake). Batch Feature Views can be scheduled to materialize new feature data to the Online and Offline Feature Stores on a regular cadence. They can also run automatic backfills when they’re first created.

note

With Tecton on Snowflake, a Batch Feature View can define a transformation against a Snowflake data source, only.

Common Feature Examples:

  • determining if a user's credit score is over a pre-defined threshold
  • counting the total number of transactions over a time window in batch
  • batch ingesting pre-computed feature values from an existing batch source

Batch Feature Transformations​

A Batch Feature View defines a transformation that turns your raw data into feature values. When Tecton executes the transformation, it always runs directly in the data platform you connected to Tecton (e.g. your Snowflake warehouse or your Databricks cluster).

from tecton import batch_feature_view


@batch_feature_view(sources=[transactions], entities=[user], mode="spark_sql")
def user_last_transaction_amount(transactions):
    return f"""
        SELECT
            USER_ID,
            AMOUNT,
            TIMESTAMP
        FROM
            {transactions}
        """

Materialization to the Online and Offline Feature Store​

Online Materialization​

You can easily make batch features available for low-latency online retrieval to feed an online model. Simply set online=True, a batch_schedule that determines how frequently Tecton runs your transformation and a feature_start_time date to backfill feature data from.

from tecton import batch_feature_view
from datetime import datetime, timedelta


@batch_feature_view(
    sources=[transactions],
    entities=[user],
    mode="spark_sql",
    online=True,
    batch_schedule=timedelta(days=1),
    feature_start_time=datetime(2020, 10, 10),
)
def user_last_transaction_amount(transactions):
    return f"""
        SELECT
            USER_ID,
            AMOUNT,
            TIMESTAMP
        FROM
            {transactions}
        """

Offline Materialization​

Tecton also supports offline materialization. This can speed up some expensive queries considerably. When you set offline=True, Tecton will materialize offline feature data to an offline table according to the batch_schedule and feature_start_time.

info

This feature is not supported in Tecton on Snowflake, except when using incremental backfills.

If you are interested in this functionality, please file a feature request.

from tecton import batch_feature_view
from datetime import datetime, timedelta


@batch_feature_view(
    sources=[transactions],
    entities=[user],
    mode="spark_sql",
    offline=True,
    batch_schedule=timedelta(days=1),
    feature_start_time=datetime(2020, 10, 10),
)
def user_last_transaction_amount(transactions):
    return f"""
        SELECT
            USER_ID,
            AMOUNT,
            TIMESTAMP
        FROM
            {transactions}
        """

If you don’t materialize Batch Feature Views offline, Tecton will always execute your transformation when you use the Tecton SDK to generate offline data. Speaking in SQL terms, a Batch Feature View without offline materialization is simply a “View”. A Batch Feature View with offline materialization is a “Materialized View”.

Offline materialization has additional benefits including:

  • Online-offline skew is minimized because the data in the online and offline store is incrementally updated at the same time.
  • Offline feature data is saved so it is resilient to any losses of historical data upstream.

Materialization Feature Data Filtering​

Every materialization run is expected to produce feature values for a specific time range. This time range is known as the “materialization window”. The materialization window is different for backfills and incremental runs:

  • During the initial backfill of feature data to the Online and Offline Feature Store, the materialization time window starts with feature_start_time and ends with Tecton’s “current wall clock time” at which the feature’s materialization is enabled.
  • On incremental runs, the materialization time window starts with the previous run’s start_time and ends with start_time + batch_schedule.

Backfill and Incremental Materialization

Tecton only materializes feature values that fall within the materialization time window. It automatically applies a filter to the Feature View transformation as shown with the WHERE clause below:

--Tecton applies this filter to the user-provided transformation

SELECT * FROM {batch_feature_view_transformation}
WHERE {timestamp_field} >= {start_time}
  AND {timestamp_field} < {end_time}
info

The start time of the window is inclusive and the end time is exclusive. This means that a feature value whose timestamp is exactly equal to the end_time is not part of the window.

Creating Efficient Transformations using Raw Data Filtering​

In many cases, running the transformation against the full set of raw data is unnecessary and inefficient. Some data platforms will push down Tecton’s feature data filter (shown above) to the raw data, only reading what is needed, but this is not always the case.

caution

We strongly recommend adding raw data filtering to Spark-based Feature Views in order to achieve good performance.

Filtering Using the Context Object​

In your Batch Feature View transformation, you can filter for the raw data needed to produce feature values on each run by leveraging a context object that Tecton passes into the transformation. context.start_time and context.end_time are equal to the expected materialization time window as shown in the diagram below:

Materialization Context Window

The example transformation below filters for the required raw data in the WHERE clause.

from tecton import batch_feature_view, materialization_context
from datetime import datetime, timedelta


@batch_feature_view(
    sources=[transactions],
    entities=[user],
    online=True,
    mode="spark_sql",
    batch_schedule=timedelta(days=1),
    feature_start_time=datetime(2020, 10, 10),
    offline=True,
)
def user_last_transaction_amount(transactions, context=materialization_context()):
    return f"""
        SELECT
            USER_ID,
            AMOUNT,
            TIMESTAMP
        FROM
            {transactions}
        WHERE TIMESTAMP >= TO_TIMESTAMP("{context.start_time}")
            AND TIMESTAMP < TO_TIMESTAMP("{context.end_time}")
        """
info

In cases where you read from a time-partitioned data source, like a Glue table or partitioned data on S3, you will also want to filter by partition columns.

Filtering Using the FilteredSource Class​

For convenience, Tecton offers a FilteredSource class that applies timestamp and partition filtering to the data source automatically based on parameters set on the Batch Data Source object: timestamp_field and datetime_partition_columns (if using Hive). This replaces the need for the WHERE clause in the transformation above. Tecton will automatically filter the data source’s data based on its timestamp_field and, if applicable, its datetime_partition_columns.

from tecton import batch_feature_view, FilteredSource
from datetime import datetime, timedelta


@batch_feature_view(
    sources=[FilteredSource(transactions)],
    entities=[user],
    mode="spark_sql",
    online=True,
    batch_schedule=timedelta(days=1),
    feature_start_time=datetime(2020, 10, 10),
    offline=True,
)
def user_last_transaction_amount(transactions):
    return f"""
        SELECT
            USER_ID,
            AMOUNT,
            TIMESTAMP
        FROM
            {transactions}
        """

By default, FilteredSource filters for data between context.start_time and context.end_time. If needed, a start_time_offset parameter can be set with a negative offset to increase the amount of raw data that gets read. For example, setting start_time_offset with a negative offset of 10 days (timedelta(days=-10)) will filter for data in the range [context.start_time - 10 days, context.end_time):

FilteredSource(transactions, start_time_offset=timedelta(days=-10))

Creating Features that use Time-Windowed Aggregations​

Using Built-in Time-Windowed Aggregations​

Tecton provides built-in implementations of common time-windowed aggregations that simplify transformation logic and ensure correct feature value computation.

For a list of available time-window aggregation functions and other information about the functions, refer to the Time-Window Aggregation Functions Reference.

Time-windowed aggregations can be specified in the Batch Feature View decorator using the aggregations and aggregation_interval parameters as shown below. Tecton expects the provided SQL query to select the raw events (with timestamps) to be aggregated.

from tecton import batch_feature_view, Aggregation, materialization_context
from datetime import datetime, timedelta


@batch_feature_view(
    sources=[transactions],
    entities=[user],
    mode="spark_sql",
    online=True,
    batch_schedule=timedelta(days=1),
    feature_start_time=datetime(2020, 10, 10),
    offline=True,
    aggregation_interval=timedelta(days=1),
    aggregations=[
        Aggregation(
            column="AMOUNT",
            function="mean",
            time_window=timedelta(days=30),
            name="average_amount_30d",
        ),
        Aggregation(
            column="AMOUNT",
            function="mean",
            time_window=timedelta(days=60),
            name="average_amount_60d",
        ),
        Aggregation(
            column="AMOUNT",
            function="mean",
            time_window=timedelta(days=90),
            name="average_amount_90d",
        ),
    ],
)
def user_transaction_features(transactions, context=materialization_context()):
    return f"""
        SELECT
            USER_ID,
            AMOUNT,
            TIMESTAMP
        FROM
            {transactions}
        WHERE TIMESTAMP >= TO_TIMESTAMP("{context.start_time}")
            AND TIMESTAMP < TO_TIMESTAMP("{context.end_time}")
        """
note

If the aggregation you need is not supported, please make a feature request or define your own custom aggregation.

How Time-Windowed Aggregations are Computed​

Behind the scenes, Tecton stores partial aggregations in the form of "tiles". The tile size is defined by the aggregation_interval parameter. At feature request-time, Tecton's online and offline feature serving capabilities automatically roll up the persisted tiles to produce the final feature value over the entire time window. This has several key benefits:

  • Significantly reduced storage requirements if you define several time windows, because all time windows will share the same underlying tiles
  • Reduced precompute resource requirements, given that Tecton needs to only compute incremental tiles and not the entire time window

Defining Custom Time-Windowed Aggregations​

If you want to use a time-windowed aggregation that is not a Tecton built-in aggregation, you can define a custom time-windowed aggregation by setting incremental_backfills=True. You can learn more about implementing this by referring to the Custom Batch Aggregations Reference. Incremental backfills cannot be used with built-in time-windowed aggregations.

Configuring a Data Source Used By a Batch Feature View to Account for Late Arriving Data​

By default, incremental materialization jobs for Batch Feature Views run immediately at the end of the batch schedule period. To override this default, set the data_delay parameter, which is specified in the data source configuration (the batch_config object referenced in the BatchSource object used by the Batch Feature View). data_delay configures how long jobs wait after the end of the batch schedule period before starting. This is typically to ensure that all data has landed. For example, if a Batch Feature View has a batch_schedule of 1 day and its data source input has data_delay=timedelta(hours=1) set, then incremental batch materialization jobs will run at 01:00 UTC.

The ttl (time-to-live) parameter​

The value of ttl (a Batch Feature View parameter) affects the availability of feature data in the online store, the generation of training feature data, and the deletion of feature values from the online store.

For more details, see The ttl Parameter in Feature Views.

Full list of parameters​

See the API reference for the full list of parameters.

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