Help Center Troubleshooting Problems with Ad Serving

Why does ad server deliver above the maximum impression limit?

In order to select each ad in less than 0.02 seconds, which is extremely fast, our ad serving engine compares the limit/target you set with a cached number that is up to a few minute-old instead of a real-time number. The reason is that getting a real-time impression counter from all ad servers around the world to compare on each impression will significantly slow down the ad selection process. Therefore, over-delivery can happen when the actual impression number delivered is a little over the specified limit in some cases. Commonly, it's within 3% of the specified target/maximum. The actual overage amount depends on the actual traffic pattern. Some common cases for this issue are described next:

Low Target/Maximum vs High Traffic

If a target/maximum value is too small (eg: 500 views per day) when comparing to a high actual traffic (eg: more than 500 views per hour), the quota will be reached very quickly. Even in these cases, our ad serving engine will stop serving the ad as soon as it determines the limit has been reached. The delay is normally within 2 minutes.

Low Hourly Quota

Hourly quota is designed to smooth out delivery evenly during the day. It should be used in conjunction with a daily quota. Please note that if the hourly quota is small while the available inventory is high, the actual impressions served might be much higher than the quota because of the delay in caching. For example, the target is set at 50 impressions/hour while the available inventory for this ad is 5000 impressions/hour. The ad will reach its target within the first few minutes or even seconds of the hour.

Unpredictable Traffic Pattern

If suddenly there is a stream of heavy traffic coming in for this ad within a minute, this might push it over the target limit. Since our system uses forecasting to understand the traffic pattern, delivery for new ads with no performance history can be a little less than accurate. If the ad is new, our system does not have any history for forecasting. It might take a couple time periods to establish a history for accurate forecasting.

Modification to Restriction Value

If the target value is modified after it has been reached, this is not an over-delivery issue but could create a confusion. For example: an ad has a quota of 2000 impressions/day. As of now, it has reached the limit for today. Then, the target is accidentally changed to 1000 impressions/day. The restriction listing would show as if it is an over-delivery issue but, in fact, it is because of the new reduced setting.

Conflicts between Restrictions

If the quota has been reached but another restriction for this ad allows it to show with an OR logic operator, this ad will continue to be served. For example: AdX has 2 restrictions. It should serve up to 1000 impressions per day OR should show to visitors from Canada. If a visitor is from Canada, the ad will show regardless of the number of impressions. In most cases, AND's should be used instead. OR's can be used with a full understanding and a full logical evaluation during the planning process by the ad team.