TTL Sweep & Expiration

ServeIndex entries have a time-to-live to prevent stale ads from serving indefinitely.

TTL Assignment

When writing auction results:

expiresAtMs = System.currentTimeMillis() + ttlDurationMs

Default TTL: 120 minutes. Under normal operation, the next auction refreshes the entry before TTL expires.

Budget Exhaustion TTL Refresh

On CampaignBudgetExhausted or AdvertiserBudgetExhausted:

expiresAtMs = System.currentTimeMillis() + (dayDurationSeconds × 1.1 × 1000)

The 1.1x factor ensures the entry survives until well past the next daily budget reset.

Periodic Sweep

From ServeIndexDData.scala:

SweepInterval = 2.minutes
MaxKeysRemovePerRun = 500

Every 2 minutes, each node scans all 32 buckets:

for each bucket:
    entries = bucket.entries
    expired = entries.filter(e => now > e.expiresAtMs)
    remove up to 500 expired entries from this bucket

Bounded Removals

The 500-per-bucket limit prevents a large batch of expirations from overwhelming DData:

32 buckets × 500 = up to 16,000 entries per sweep
In practice, expirations are spread across time, so batches are smaller

Why Not Instant Expiration?

Approach	Problem
Instant expiry	Clock skew between nodes → entries flicker
Individual removes	Many small deltas → gossip overhead
Batched sweep	Predictable load, clock-skew tolerant

The 2-minute sweep interval means an expired entry might serve for up to 2 extra minutes. This is acceptable — the pacing gate and budget checks provide additional safety at serve time.