Frequency cap = 5, Duration = 1 day
impression) by the same user maximum 5 times a day. From advertiser side, the unique users who sees the ad will increase by setting up the frequency cap.
Average frequency=1.5It means on average all audiences have seen the ad 1.5 times.
bid-serversto follow. In the above example, target frequency for campaign 1234
maxFreqCampaign_is shared using redis, written to master makes it available to all the slaves immediately (eventually consistent). And each bid-servers has to follow the given target for the campaign.
wait-time, bigger the risk. However, usually impression notification will be received by server within few seconds for 95-98% of the time.
Wait-timedelays the counter to update, so during this wait-time if same user appears again, bidder-server may send the same advertisement again. But it's very unlikely to happen that often hence this is one of the balanced good solution to go with.