# Logging and metrics for overlay ads in MediaTailor
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This section explains logging and metrics for overlay ads in MediaTailor. For more information about setting up logging, see [Monitoring and tagging AWS Elemental MediaTailor resources](monitoring.md).

**Topics**
+ [CloudWatch logs](#overlay-ads-logging-and-metrics-cloudwatch)
+ [CloudWatch metrics](#overlay-ads-logging-and-metrics-cloudwatch-metrics)

## CloudWatch logs
<a name="overlay-ads-logging-and-metrics-cloudwatch"></a>

CloudWatch collects the following log information about overlay ads:
+ `VAST_RESPONSE` - Shows information about the non-linear ads list.
+ `FILLED_PROVIDER_OVERLAY` - Shows information about the non-linear ads.

**Note**  
The `RAW_ADS_RESPONSE` is an optional event that shows the original response from the ADS. Using this event is especially helpful in a staging and testing environment. To enable this event on a configuration or account, submit a ticket to AWS Support.

## CloudWatch metrics
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MediaTailor collects overlay ad metrics separately from other ADS metrics. MediaTailor collects these metrics after successfully fetching the ads from the ADS. You don't have to poll the `GetTracking` API to collect the metrics.

The following table describes CloudWatch metrics for overlay ads:


| Metric | Description | 
| --- | --- | 
| AdDecisionServer.OverlayAds | The count of overlay ads included in the ADS responses within the CloudWatch time period that you specified. | 
| AdDecisionServer.OverlayErrors | The number of non-HTTP `200` status code responses, empty responses, and timed-out responses that MediaTailor received from the ADS within the CloudWatch time period that you specified. | 
| AdDecisionServer.OverlayFilled | The number of avails that were successfully filled with at least one overlay ad:[See the AWS documentation website for more details](http://docs.aws.amazon.com/mediatailor/latest/ug/overlay-ads-logging-and-metrics.html)<br />`SampleCount` tracks the number of avails filled.<br />`Sum` tracks the number of successfully filled overlay avails. | 
| AdDecisionServer.OverlayMinSuggestedDuration | The sum of `minSuggestedDuration` durations, in milliseconds, of all ads that MediaTailor received from the ADS within the CloudWatch time period that you specified. If `minSuggestedDuration` isn't specified, the duration shown is the planned duration. | 
| AdDecisionServer.OverlayLatency | The response time, in milliseconds, for requests that MediaTailor makes to the ADS. | 
| AdDecisionServer.OverlayTimeouts | The number of timed-out requests to the ADS in the CloudWatch time period that you specified. | 
| AdsBilled | For more information about ads billed, see [Billing for overlay ads in MediaTailor](overlay-ads-billing.md). | 
| Avail.\* | Because MediaTailor doesn't do any planning for overlay ads, CloudWatch doesn't show any `Avail.X` metrics. | 
| SkippedReason.\* | Because MediaTailor doesn't do any planning for overlay ads, CloudWatch doesn't show any `SkippedReason.X` metrics. |