Turnning a Redemption Queue into a Numeric Comparison with Mathematical Accumulation in a Stablecoin Project

If you’ve ever shipped a stablecoin (or any on-chain redemption / withdrawal flow), you’ll eventually meet the same throughput killer: the queue. At low load it “works.” Then traffic spikes: gas spikes, txs fail, latency climbs, an operator is forced to “clear the queue,” and the team gets dragged into hotfix mode.

Here’s a pattern we used at Cyberk while optimizing redemption for a stablecoin backed by $USDT/$USDC: transform a "Queue Management" problem into a simple "Numeric Comparison" by applying Mathematical Accumulation Functions. It’s pragmatic because it helps you:

• collapse procedural loops into number comparisons (O(1))
• enforce FIFO as a mathematical invariant (instead of pointer/index choreography)
• reduce attack surface (fewer state-transition branches)

Note: every math/formula line below is copied verbatim from the source, with zero symbol changes, so PDF rendering won’t “break.”

1) The procedural queue problem: “correct logic,” wrong throughput

Most dApps handle redemption with a procedural queue: store each request in an array/linked list, and when new collateral arrives (deposit/disbursement), the contract/operator loops through requests to update status and claimable balances.

You’ll see this pattern everywhere (and it often balloons fast):

• OpenZeppelin Standard: Using DoubleEndedQueue, which requires manual management of pointers and array storage.
• Lido/Ondo Finance: Their implementations (e.g., WithdrawalQueue.sol) often exceed 1,000 lines of code. These contracts must handle complex logic to iterate through requests, update individual statuses, and manage pointers.

The issue isn’t that the devs are “bad.” It’s structural: a procedural queue forces you to walk per-request state. Two major costs:

• Linear Gas Growth ($O(n)$): To clear the queue, an operator must loop through individual requests. If a request is at position $100$ in the sequence, the system must process 99 preceding requests before reaching it. This is an immense bottleneck on Ethereum or Solana.
• Security Risk: More lines of code mean a larger attack surface. Procedural queues are prone to edge-case bugs during state transitions and complex pointer updates.

Under deadline pressure, the trap is predictable: the more you “optimize” a procedural queue, the more code you add (more branches), and the harder it becomes to audit and benchmark the right thing.

2) Reframe: from “managing the queue” to “comparing two numbers”

The leverage comes from changing the question. Instead of “which request has been processed?”, ask:

• how far has total collateral been disbursed?
• where does this request sit on the cumulative redemption axis?

That’s why we do it like this:

We transform a "Queue Management" problem into a simple "Numeric Comparison." By applying Accumulation Functions, we achieve $O(1)$ complexity—meaning the system cost remains constant whether there are 10 or 10,000,000 requests.

In short: you turn the queue into a number line. Each request occupies a “window” on that line. Settlement becomes comparing a window against “how far capital has flowed.”

3) Defining the Variables:

Let $t$ represent the sequence of transactions.

• $r_i$: The amount of tokens in the $i$-th Request.
• $d_j$: The amount of collateral disbursed by the Admin in the $j$-th Deposit.
• $R(n)$: The Cumulative Redemption Function for the first $n$ requests.

$R(n) = \sum_{i=1}^{n} r_i$

• $D(m)$: The Cumulative Disbursement Function after $m$ deposits.

$D(m) = \sum_{j=1}^{m} d_j$

Request Snapshotting:

When a new request $n$ is created, the contract takes a "Snapshot" of the total accumulated requests at that moment. This snapshot $S_n$ defines the exact threshold of disbursed capital required for this specific request to be settled:

Request Snapshot: $S_n = R(n)$

The specific liquidity window occupied by request $n$ is defined by the interval $[R(n-1), R(n)]$.

Settlement & Withdrawal Conditions:

A request $n$ can be settled in full if and only if the current cumulative disbursement meets its snapshot:

Full Withdrawal Condition: $D_{current} \ge S_n$

Partial Withdrawal (Pro-rata Settlement): If the disbursement has entered the request's window but hasn't cleared it ($S_{n-1} < D_{current} < S_n$), the claimable amount $\Delta$ is: $\Delta = D_{current} - S_{n-1}$

4. Why This Model is Superior

• Instant Efficiency ($O(1)$): There is no need to loop through thousands of requests. The contract only compares two numbers: **Total_Disbursed **vs Request_Snapshot.
• Absolute Fairness (True FIFO): First-In, First-Out is a mathematical certainty. Since $S_n$ is strictly increasing based on the request sequence, they are settled in the exact order they were created.
• Maximum Gas Efficiency: Replacing dynamic arrays and pointers with a single uint256 accumulation variable saves up to 80% in gas costs compared to traditional models.
• Minimalist Security: We eliminated the complex "Queue Logic" where most bugs hide. In our system, Math is the Auditor.

5) Closing: sometimes the biggest performance win is a conceptual reframing

This is the trade-off I’ll take under deadline pressure: instead of adding more code to “optimize the queue,” change the model so the queue disappears.

Key message:

• transform a "Queue Management" problem into a simple "Numeric Comparison"
• use Mathematical Accumulation Functions to make FIFO an invariant
• get $O(1)$ hot-path cost and a smaller bug surface

If your system has a queue (withdrawals, redemptions, batch settlements…), ask yourself: are you paying for the nature of the problem—or for the data structure you chose?