# Freshness anomalies

The `elementary.freshness_anomalies` test monitors the freshness of your table over time, measuring the expected time between data updates.\
Monitors the freshness of your table over time, as the expected time between data updates.

### How it works

1. Data is split into time buckets (daily by default, configurable with the `time_bucket` field).
2. The maximum freshness value is computed per bucket for the last `training_period` (14 days by default).
3. The test compares the freshness of each bucket within the detection period (last 2 days by default, controlled by the `detection_period` var) to the freshness of previous time buckets.
4. If any anomalies are detected during the detection period, the test will fail.

{% tabs %}
{% tab title="Models" %}

```yml
models:
  - name: < model name >
    tests:
      - elementary.freshness_anomalies:
          timestamp_column: < timestamp column > # Mandatory
          where_expression: < sql expression >
          time_bucket: # Daily by default
            period: < time period >
            count: < number of periods >
```

{% endtab %}

{% tab title="Models example" %}

```yml
models:
  - name: login_events
    tests:
      - elementary.freshness_anomalies:
          timestamp_column: "updated_at"
          # optional - use tags to run elementary tests on a dedicated run
          tags: ["elementary"]
          config:
            # optional - change severity
            severity: warn
```

{% endtab %}
{% endtabs %}

## Test configuration <a href="#test-configuration" id="test-configuration"></a>

```yaml
tests:
  — elementary.freshness_anomalies:
    timestamp_column: column name
    where_expression: sql expression
    anomaly_sensitivity: int
    detection_period:
      period: [hour | day | week | month]
      count: int
    training_period:
      period: [hour | day | week | month]
      count: int
    time_bucket:
      period: [hour | day | week | month]
      count: int
    detection_delay:
      period: [hour | day | week | month]
      count: int
    ignore_small_changes:
      spike_failure_percent_threshold: int
      drop_failure_percent_threshold: int
    anomaly_exclude_metrics: [SQL expression]
```

{% hint style="warning" %}

#### Notes:

* **Required Configuration**: `timestamp_column`&#x20;
* **Default configuration***:* `anomaly_direction: spike` to alert only on delays.
  {% endhint %}