# Time to live (TTL) duration for records
<a name="feature-store-time-to-live"></a>

Amazon SageMaker Feature Store provides the option for records to be hard deleted from the online store after a time duration is reached, with time to live (TTL) duration (`TtlDuration`). The record will expire after the record’s `EventTime` plus the `TtlDuration` is reached, or `ExpiresAt` = `EventTime` \$1 `TtlDuration`. The `TtlDuration` can be applied at a feature group level, where all records within the feature group will have the `TtlDuration` by default, or at an individual record level. If `TtlDuration` is unspecified, the default value is `null` and the record will remain in the online store until it is overwritten. 

A record deleted using `TtlDuration` is hard deleted, or completely removed from the online store, and the deleted record is added to the offline store. For more information on hard delete and deletion modes, see [https://docs.aws.amazon.com/sagemaker/latest/APIReference/API_feature_store_DeleteRecord.html](https://docs.aws.amazon.com/sagemaker/latest/APIReference/API_feature_store_DeleteRecord.html) in the Amazon SageMaker API Reference guide. When a record is hard deleted it immediately becomes inaccessible using Feature Store APIs.

**Important**  
TTL typically deletes expired items within a few days. Depending on the size and activity level of a table, the actual delete operation of an expired item can vary. Because TTL is meant to be a background process, the nature of the capacity used to expire and delete items via TTL is variable (but free of charge). For more information on how items are deleted from a DynamoDB table, see [How it works: DynamoDB Time to Live (TTL)](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/howitworks-ttl.html).

`TtlDuration` must be a dictionary containing a `Unit` and a `Value`, where the `Unit` must be a string with values "Seconds", "Minutes", "Hours", "Days", or "Weeks" and `Value` must be an integer greater than or equal to 1. `TtlDuration` can be applied while using the `CreateFeatureGroup`, `UpdateFeatureGroup`, and `PutRecord` APIs. See the request and response syntax in the SDK for Python (Boto3) documentation for [https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker/client/create_feature_group.html#SageMaker.Client.create_feature_group](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker/client/create_feature_group.html#SageMaker.Client.create_feature_group), [https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker/client/update_feature_group.html](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker/client/update_feature_group.html), and [https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker-featurestore-runtime/client/put_record.html#](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker-featurestore-runtime/client/put_record.html#) APIs.
+ When `TtlDuration` is applied at a feature group level (using the `CreateFeatureGroup` or `UpdateFeatureGroup` APIs), the applied `TtlDuration` becomes the default `TtlDuration` for all records that are added to the feature group *from the point in time that the API is called*. When applying `TtlDuration` with the `UpdateFeatureGroup` API, this will *not* become the default `TtlDuration` for records that were created *before* the API is called.

  To remove the default `TtlDuration` from an existing feature group, use the `UpdateFeatureGroup` API and set the `TtlDuration` `Unit` and `Value` to `null`.
+ When `TtlDuration` is applied at a record level (for example, using `PutRecord` API), the `TtlDuration` duration applies to that record and is used instead of the feature group level default `TtlDuration`.
+ When `TtlDuration` is applied on a feature group level it may take a few minutes for `TtlDuration` to come into effect.
+ If `TtlDuration` is used when there is no online store, you will receive a `Validation Exception (400)` error. 

The following example code shows how to apply `TtlDuration` while updating a feature group, such that the records added to the feature group *after running the API *will by default expire four weeks after their event times.

```
import boto3

sagemaker_client = boto3.client("sagemaker")
feature_group_name = '<YOUR_FEATURE_GROUP_NAME>'

sagemaker_client.update_feature_group(
    FeatureGroupName=feature_group_name,
    OnlineStoreConfig={
        TtlDuration:{
            Unit: "Weeks",
            Value: 4
        }
    }
)
```

You can use the `DescribeFeatureGroup` API to view the default `TtlDuration`. 

To view the expiration times, `ExpiresAt` (in UTC time ISO-8601 format), while using the `GetRecord` or `BatchGetRecord` APIs you must set `ExpirationTimeResponse` to `ENABLED`. See the request and response syntax in the SDK for Python (Boto3) documentation for [https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker/client/describe_feature_group.html#describe-feature-group](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker/client/describe_feature_group.html#describe-feature-group), [https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker-featurestore-runtime/client/get_record.html#get-record](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker-featurestore-runtime/client/get_record.html#get-record), and [https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker-featurestore-runtime/client/batch_get_record.html#batch-get-record](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sagemaker-featurestore-runtime/client/batch_get_record.html#batch-get-record) APIs.