The ckBAT Index Upgrade Targets a Hidden Failure Mode: Reserved Cycles

The Internet Computer’s ckBAT index canister is receiving a larger safety margin for storage reservation—not additional operating funds.

NNS proposal 143967, published on September 15, proposes raising the reserved_cycles_limit for canister jywzd-7aaaa-aaaar-qcbeq-cai from the default 5 trillion cycles to 1,000,000,000,000,000,000 cycles. The proposal says the change neither reserves nor spends cycles; it only increases the ceiling on the canister’s secondary reserved-cycles balance.

That distinction matters for Chain Fusion infrastructure. When a subnet is under storage pressure, the protocol can move cycles from a canister’s main balance into reserved cycles to cover future memory payments. The official management-canister specification says an operation that would push reserved_cycles above its configured limit fails. A low ceiling can therefore prevent a canister from growing even when its overall balance is otherwise sufficient.

The proposal identifies the current 5T setting as the practical bottleneck. On the 34-node fiduciary subnet, it estimates that the worst-case reservation rate would consume roughly 249T cycles per GiB, meaning the default limit covers only about 20 MiB of additional growth. The proposed limit is intended to exceed the maximum reservation the protocol could demand on that subnet.

This is a reliability change at the resource-accounting boundary. It does not pre-fund the index, increase its memory allocation, or guarantee unlimited storage. Reservations remain constrained by the canister’s actual cycle balance and by subnet capacity. ICP’s documentation also notes that reservation costs arise when subnet usage exceeds 750 GiB and scale toward projected payments at full capacity.

The canister is managed by the ledger suite orchestrator, while NNS root is listed as a co-controller. That controller arrangement explains why the proposal changes the setting directly rather than routing the update through the orchestrator.

The proposal does not disclose the ckBAT index canister’s current memory usage or cycle balance, so this should be read as capacity protection, not evidence of imminent exhaustion. A related proposal, NNS 143966, addressed the reserved-cycles limit of the ckBAT ledger canister, indicating a broader maintenance pass across the ckBTC-style asset infrastructure.