Ads Frequency Cap

An Ads Frequency Cap system limits how many times a user sees a specific ad or ad category within a given time window. This is crucial for advertisers—showing the same ad too many times leads to user fatigue and wasted impressions, while showing it too few times means missed opportunities.

Unlike a standard Rate Limiter, ads frequency capping has a unique characteristic: the read and write paths are separated. During ad bidding, you check if an ad is eligible (read), but a successful bid doesn't mean the ad gets shown. The actual impression is recorded later through event tracking (write). This separation fundamentally changes the design.