hardDesignScenarioMidSeniorStaff
A family plan shares 100 GB across five SIMs with each SIM capped at 30 GB. How does charging enforce both limits at once?
6 min readUpdated 2026-08-15
Answer
Short answer
Every reservation must decrement the shared pool and the member's own counter atomically, granting the smallest of the two remainders. That makes the group rather than the subscriber the serialisation point, and it means a member with headroom can still be refused because the pool is gone.
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Likely follow-ups
- A member's session dies holding a reservation. How do the pool and their own counter recover?
- Offline records for one member arrive two days late. Who should have been throttled?
- A sixth SIM joins on day twenty. How much of the pool does it get, and why?
- The account holder wants to raise one member's cap mid-period. What has to happen?
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