How line item delivery is paced

Learn how Ad Manager decides to delivery line items

Pacing is the rate at which Ad Manager delivers impressions for a line items. Ad Manager distributes impression delivery based on both the Deliver impressions setting for the line items and Ad Manager pacing rules that attempt to optimize delivery. This article describes how line item settings and these Ad Manager pacing rules affect impression delivery.

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Use a line item's "Troubleshoot" tab to see reasons your line item isn't delivering. This can help you determine whether your delivery settings need to be adjusted to optimize revenue.

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General pacing rule

When a line item starts, Ad Manager determines delivery pacing for the line item to ensure it meets its goal. Pacing is affected by the "Deliver impressions" setting for the line item, which allows you to indicate how you want to distribute impressions for a line item over its lifetime.

For line items whose "Deliver impressions" are set to either Frontloaded or Evenly, Ad Manager divides the number of impressions booked for a given line item by the number of days a the line item is set to run.

"Expected traffic shape"

"Expected traffic shape" optimizes how line items deliver based on traffic patterns of your website. If enabled, Ad Manager tries to deliver more impressions when traffic is high and fewer when traffic is low. As a result, even if a line item is set to Evenly, you might notice that absolute number of impressions isn't always identically distributed over time. Learn more

View example and illustration

If there were a line item with 7,000 booked impressions that runs for 7 days, whose "Deliver impressions" is set to Evenly, Ad Manager would schedule 1,000 impressions per day.


7,000 impressions booked running over 7 days would be scheduled for 1,000 impressions per day

Expected traffic shape

"Expected traffic shape" is a network-wide feature that uses past traffic patterns of your website to predict traffic trends and pace delivery accordingly. Check with your administrator if you're not sure that this feature is enabled in your network.

"Expected traffic shape" versus forecasting

"Expected traffic shape" is different from forecasting. Forecasting considers future, competing line items to determine availability of inventory for a line item. "Expected traffic shape" simply looks at visits to your website to understand when traffic is higher or lower in order to distribute impressions for line items more optimally.

"Expected traffic shape" allows Ad Manager to deliver impressions smoothly relative to the natural traffic fluctuations on your site. There are two ways that "expected traffic shape" analyzes traffic:

  • Line items running less than two weeks: average of your network's overall past traffic patterns determines when to deliver more or fewer impressions.

  • Line items running two weeks or more: traffic patterns specific to the inventory a line item targets determines when to deliver more or fewer impressions.
View example and illustration

Example one—line item runs less than two weeks

Suppose you have a new line item that just started today. Ad Manager uses the average of past traffic patterns for your website to determine when to deliver more or fewer impressions for the line item.

This illustration below is an example of how Ad Manager predicts future traffic patterns for a website based on the the past four weeks of traffic patterns. The new line item would the deliver according to that prediction.

  • Average pageviews on your website over the past 4 weeks
  • New line item delivers based on average pageviews
Mon Tue Wed Thu Fri Sat Sun

 

Example two—line item runs two weeks or more

After a line item runs for two weeks, Ad Manager does a similar analysis based on the specific inventory a line item targets. Instead of website averages, Ad Manager uses averages for the inventory targeted by the line item. and looks back up to 4 weeks if the line item runs long enough.

  • Average pageviews for inventory targeted by line item running 2 weeks or more
  • Line item delivers based on pageviews for inventory targeted
Mon Tue Wed Thu Fri Sat Sun

For instance, suppose the line item targeted the sports inventory of your website, and currently the Olympic Games were underway. Your sports inventory is getting exceptionally higher traffic currently as a result. Most of it starts to peak approaching the weekend and peaks during the weekend. As a result, Ad Manager optimizes line item delivery to the sports inventory according to this past traffic pattern.

Early distribution of impressions

Next Ad Manager applies a frontloading factor to the line item goals. As described above for frontloaded line items, this factor can be as high as 40% at any one time, but averages to 25% over the course of the first half of the campaign. This compares to about 5% above goal during the first half of a campaign for even delivery.

These frontloading factors are applied on an iterative basis, which means that an even delivery line item on the first day will serve 5% higher than the delivery goal. On the second day the line item will serve 5% higher than the goal for the second day, where the second day goal is slightly lower than the first day goal due to the 5% addition on day one.

This continues through the life of the line item such that, all other factors being equal, there is a small decrease in the impressions served each day. For line items set to "Evenly," this decrease will be very small in most cases. For line items set to "Frontloaded," it will be more apparent.

Line items with low delivery goals

Line items with very low goals do not begin to deliver immediately and may have fluctuating delivery over its lifetime. A low delivery goal would result in a daily goal of of approximately 24 impression. 

View illustration

Frontloaded adserving vs. even vs. none

When a line item is set to deliver evenly, the ad server is only allowed to exceed the daily goal by 5%. For frontloaded delivery, the ad server can exceed the goal by as much as 40% at any one time, but averages to 25% over the first half of a campaign, and returns to evenly delivered during the second half. This results in more impressions being served toward the beginning of the campaign than would serve with perfectly even delivery, and fewer being served at the end. This helps ensure that delivery doesn’t fall short of the line item's goal due to lack of inventory at the close of the campaign.

Applying this frontloading factor to our running example we get the serving goals illustrated in Chart 4.


When ad serving combines traffic shape (if enabled for your network) with frontloading, delivery will align with traffic patterns but will exceed the goal briefly by as much as 40%, and 25% during the first half of a campaign. Again, the result is that more impressions are served toward the beginning of the campaign to avoid falling short at the last moment.

Changes over time

Over time Ad Manager has to adjust the goals for your line item based on the actual number of impressions it has served. The originally calculated goals, as outlined above, are only valid when the server delivers exactly to the goal every hour.

Review each step below to see which calculations are updated and modified throughout delivery.

1. Satisfaction Index

Ad Manager calculates a satisfaction index (SI) to measure how far ahead or behind schedule a line item is. Specifically SI measures how well a line item has performed over the last 24 hours, relative to the goals set for it by the ad server. The SI is then used during the line item selection process so that line items that are further behind are selected more frequently. If you are not generally familiar with SI and how it is used in the line item selection process, please see the ad selection whitepaper in this help center for more information.

2. SI threshold

Rather than selecting a line item directly based on SI, Ad Manager instead sets a different threshold for each line item. The SI for the line item must exceed this threshold in order for the ad server to select it amongst all of the line items that accepted the ad server's request. This threshold is also calculated once an hour and is controlled by the Proportional Integral Derivative (PID) controller.

The PID controller attempts to make a line item react more gradually to changes in its environment such as unexpected changes in your site’s traffic levels. Instead of dramatically decreasing the threshold every time the SI starts to fall, the PID controller instead takes a more gradual approach. When setting the threshold it considers both how far away the line item is from a perfect SI and how quickly the SI of the line item is changing. The net effect is that your line items will deliver more evenly than they did in the ad server.

Since the PID controller’s adjustments are gradual, it will take your line item several hours to fully correct if it gets ahead or behind. Although this may seem odd in the short term, it significantly improves delivery over the life of the line item.

3. Delivery goal recalculation

Ad Manager regularly recalculates the daily and hourly delivery goals. This follows the same process outlined for a new line item above, but uses updated information. Impressions are allocated based on the total remaining impressions and the total remaining time in the line item's campaign. For line items that have been live less than 24 hours, these delivery goals are updated every hour. After the first day the delivery goals are updated every eight hours. The goals are updated more frequently for new line items to allow the server to calibrate itself based on how the new line item is delivering.

If a line item has fallen behind schedule or has been paused for a period of time, then begins delivering again, Ad Manager tries to make up the missing impressions during the next 24 hours, then deliver the remaining impressions evenly over the remaining days (assuming that the line item is set to deliver evenly).

For example, a line item has an impression goal of 100,000 over 10 days. The line item delivers its goal of 10,000 impression on each of the first two days, then is paused for four days. On the seventh day, the line item is restarted; it has 80,000 impressions still to deliver. Ad Manager will try to deliver approximately 50,000 impressions on the seventh day: 10,000 impressions for each day that the line item was paused, plus 10,000 impressions for the current day. (Because of the 5% frontloading that's applied to line items set to spread evenly, the exact impression goal for each day would vary.)

4. Updated by expected traffic shape in pacing

If your network is enabled to pace based on expected traffic (see the section above), the ad server also takes hints from past delivery patterns when determining how many times to serve a line item in a given time window.

For networks that are enabled to pace based on expected traffic, OSI will take the traffic-shaped ad server goals into account and will represent a more accurate measure of delivery status. Still, always be sure to check the forecast for a line item before making any delivery changes.

If you recently created your Ad Manager network, wait at least one month before requesting that this feature be enabled.

5. End-of-campaign behavior

During the final six hours of a fixed-goal line item that hasn't yet reached its goals, Ad Manager begins adjusting the PID controller to ensure that the goal is met. In the last hour, a line item that still needs to deliver impressions will function as if it were set to deliver as fast as possible.

If a campaign is behind schedule, it may even serve ahead of higher-priority campaigns that have recently started delivering and are expected to deliver in full.

Why did my line item exceed its limit?

A line item's delivered impressions total might exceed the daily or lifetime cap by a small amount due to delayed impression counting or simultaneous requests that occur as the cap is reached.

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