Reserved capacity is billed and settled per second. Not per minute, not per
interval, not against a GB-second budget. At each second t within an
interval:
if usage(t) ≤ reservedGb: that second’s memory is covered by your
reservation and billed at the reserved rate
if usage(t) > reservedGb: the part above the ceiling is overage, billed
at the on-demand rate
Per 15-minute interval, per (org, resource):
reservedBilled = reservedGb × 900 sec (the commitment, regardless of usage)overageBilled = ∑_t max(usage(t) − reservedGb, 0) (per-second integration)
Two charges, computed independently:
Reserved: a flat reservedGb × 900 GB-seconds, billed every interval
at the reserved rate, whether you used it or not. That’s the commitment.
Overage: whatever exceeded the reserved ceiling at any instant,
summed second by second, billed at the on-demand rate.
There is no draw-down, no carry-forward, no averaging. The ceiling is
re-checked every second.
You reserve 16 GB for 02:00–02:15. Your sandboxes use:
Phase
Duration
Memory
1
600 s
8 GB
2
60 s
30 GB
3
240 s
0 GB
Each second is settled against the 16 GB ceiling:
Phase
Reserved per s
Overage per s
Reserved GB·s
Overage GB·s
1
8
0
4 800
0
2
16
14
960
840
3
0
0
0
0
Bill for the interval:
Charge
GB-seconds
Rate
Reserved (commitment)
14 400
reserved
Overage
840
on-demand
You pay the full 14 400 GB-seconds (16 × 900) for the reservation
regardless of consumption. The 60-second spike to 30 GB produced 840
GB-seconds of overage on top, calculated second by second.
Usage stays below the ceiling. Reserve 16 GB, run 4 GB throughout.
Reserved = 14 400 GB·s (commitment, paid in full). Overage = 0. The unused
capacity is the cost of optionality you gave up.Usage stays above the ceiling. Reserve 16 GB, run 24 GB throughout.
Reserved = 14 400 GB·s. Overage = 8 × 900 = 7 200 GB·s.Usage averages below the ceiling but spikes above. Reserve 16 GB, run
4 GB for 800 s then 25 GB for 100 s. Average is 6.8 GB — under
reservation. The 100 s above the ceiling still produces 9 × 100 = 900
GB·s of overage. The ceiling is checked every second; averages are
irrelevant.
A GB-second budget would let arbitrary spikes ride for free as long as
quiet time balanced them out. That’s burstable behavior, not
committed-capacity behavior, and it creates incentives for adversarial
spike patterns.Per-second settlement matches what the reservation actually is: at every
moment, the ceiling is what you committed to. Above it is overage. Below
it is covered.
