Grace Periods & Hybrid Modes

PI control needs stable input signals. During startup and after periods of inactivity, signals are noisy or meaningless. Grace periods protect the controller during these transients.

Grace Period: No Serving

During grace, the throttle probability is set to MaxThrottleProb = 0.99 — effectively no serving. This is the opposite of what you might expect: rather than serving freely during warmup, Promovolve suppresses serving until it has enough data to pace correctly.

Why suppress, not serve freely? Free serving during startup could exhaust the budget before the PI controller activates. The 0.99 throttle (not 1.0) lets through ~1% of requests as “sensors” to build rate data.

Grace Period Conditions

Grace is active until both conditions are met:

graceSeconds = max(MinGraceSeconds, DefaultGracePeriodFraction × dayDurationSeconds)
             = max(10.0, 0.01 × dayDurationSeconds)

graceRequests = MinGraceRequests = 10

Grace ends when:
  elapsedSeconds >= graceSeconds AND requestCount >= graceRequests

Additionally, the EMA needs EmaStabilizationWindows = 3 windows of data to stabilize.

Staleness Reset

If no requests arrive for a configurable period, grace re-enters:

staleThreshold = BaseStaleRateThresholdMs = 30,000ms
                 (scaled proportionally for simulated short days)
                 (min: MinStaleRateThresholdMs = 1,000ms)

if (nowMs - lastRequestMs) > staleThreshold:
    resetGracePeriod()

Why? After 30 seconds of silence, the EMA-smoothed rate has decayed and no longer represents current traffic. PI corrections with stale rate data would produce erratic throttle swings.

Grace Period Constants

Constant	Value	Purpose
`DefaultGracePeriodFraction`	0.01 (1% of day)	Base grace duration
`MinGraceSeconds`	10.0	Minimum grace regardless of day length
`MinGraceRequests`	10	Minimum requests before PI activates
`MaxGraceRequests`	50	(Not currently used as lower bound)
`EmaStabilizationWindows`	3	EMA warmup windows
`BaseStaleRateThresholdMs`	30,000	Staleness detection
`MinStaleRateThresholdMs`	1,000	Min staleness for short simulated days
`MaxThrottleProb`	0.99	Throttle during grace

Grace Period Timeline

Time    Event                       Mode           Throttle
00:00   Site pacing starts          Grace          0.99 (~1% through)
00:05   5 requests arrived          Grace (count)  0.99
00:10   10s elapsed, 10+ requests   Grace (EMA)    0.99
00:13   3 EMA windows stable        PI active      Computed
...
01:30   No requests for 35s         Stale reset    0.99
01:31   Requests resume             Grace          0.99
01:41   Grace conditions met        PI active      Computed

Simulated Days

For testing and simulation, dayDurationSeconds can be set shorter than 86400 (e.g., 600 seconds for a 10-minute “day”). Grace periods, stale thresholds, and the RL observation interval all scale proportionally, ensuring the system behaves consistently regardless of the simulated time scale.

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