Lazy Evaluation
Understanding how Lazy Evaluation optimizes gas costs and improves efficiency in the Fixed-Rate Lending Protocol
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Understanding how Lazy Evaluation optimizes gas costs and improves efficiency in the Fixed-Rate Lending Protocol
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Secured Finance has introduced a revolutionary feature known as "lazy evaluation," which significantly streamlines the management of orders and the auto-roll process. This mechanism works by deferring the computation and update of orders and positions until absolutely necessary. As a result, it eliminates the need to manually roll over each position or update a multitude of open orders whenever an order is filled. This approach not only leads to substantial savings in gas costs but also boosts the overall efficiency of the protocol.
Lazy Evaluation defers computations until they are absolutely necessary, significantly reducing gas costs and improving protocol efficiency.
Orders in the system can exist in three states, all of which utilize Lazy Evaluation:
Open Order: Remaining Orders which are not filled on our orderbook system.
Active Position (FV): Once Orders are filled, they will be managed by Future Value (FV).
Auto-rolled Position (GV): Positions that have reached their maturity date will be Auto-rolled without any action and managed by Genesis Value (GV).
Lazy evaluation is utilized for all states above. For Open Orders, the contract checks if the order has been unlinked on the red-black tree, indicating that the order has already been filled. As for Active Positions (FV), if the positions reach their maturity date, they are then treated as Auto-rolled Positions (GV) and returned as such. As for Auto-rolled Positions (GV), only borrowing positions will increase after each roll. (Please refer to the for more detail)
Lazy evaluation continues to be applied to these data as long as they exist. However, when a CleanUp process is executed, the state of the data changes, and they are no longer subject to lazy evaluation once it turned to GV. CleanUp processes are implicitly executed during certain operations taken by users such as order execution, collateral withdrawals, and so on.
The above states are stored on the smart contract storage, ensuring data integrity and consistency. When a user calls the smart contract to retrieve their own amount, the system calculates the actual amount in real-time, providing up-to-date and accurate information.
Lazy order evaluation is a critical component for supporting essential functionalities such as market orders and auto-roll. Without it, executing these operations would result in substantial gas costs, particularly in terms of storage. By adopting lazy evaluation, Secured Finance streamlines its platform and ensures a more cost-effective and user-friendly experience for all participants.
Order States
Number of possible states for orders in the system
3 (Open Order, Active Position, Auto-rolled Position)
CleanUp Trigger
Operations that trigger the CleanUp process
Order execution, collateral withdrawals, etc.
Calculation Timing
When actual values are calculated
Real-time, only when requested
Storage Optimization
How storage is optimized for gas efficiency
Recycling of mature market contracts
Evaluation Method
How order and position values are determined
Deferred until necessary
Gas Savings
Typical gas savings compared to eager evaluation
40-60%
Maximum Orderbooks
Maximum number of orderbooks per currency
9 (8 active, 1 inactive)
State Transition
When positions transition between states
At maturity or when orders are filled
Let's consider how lazy evaluation works for open orders:
Alice places a limit order to lend 1,000 USDC at 5% APR in the JUN2025 market
Bob places a market order to borrow 500 USDC, which partially fills Alice's order
Without lazy evaluation, the system would need to:
Update Alice's order to show 500 USDC remaining
Create a new position record for the filled portion
Update multiple storage slots, costing significant gas
With lazy evaluation:
The system marks Alice's order as "unlinked" in the red-black tree
When Alice queries her position, the contract calculates in real-time:
Original order: 1,000 USDC
Filled amount: 500 USDC
Remaining: 500 USDC
No storage updates are needed until Alice takes an action like withdrawing funds
Result: Gas costs are reduced by approximately 60% compared to eager evaluation
Consider a scenario with auto-rolling positions:
Charlie has a lending position of 2,000 USDC in the MAR2024 market
When MAR2024 reaches maturity:
Without lazy evaluation: The system would need to update all positions in the MAR2024 market, potentially thousands of transactions
With lazy evaluation: No immediate updates occur
When Charlie checks his position after maturity:
The system detects the maturity date has passed
It automatically treats the position as an Auto-rolled Position (GV)
It calculates the new position value based on the auto-roll price
When Charlie eventually withdraws or modifies his position:
Only then is the CleanUp process executed
The position is formally updated in storage
Result: The protocol saves massive amounts of gas by avoiding unnecessary updates to all positions at maturity
The protocol further optimizes gas usage through market recycling:
The protocol has 9 orderbooks for ETH (8 active, 1 inactive)
When the MAR2024 market matures:
The market contract is not discarded but recycled
It becomes the new inactive market (which will eventually be MAR2026)
This recycling process:
Avoids the high gas cost of deploying new contracts
Maintains a fixed number of markets to evaluate
Keeps the lazy evaluation process efficient
A user with positions across multiple maturities benefits from:
Consistent gas costs regardless of how many markets are active
Predictable behavior when markets mature
Efficient position management across the entire protocol
Lazy Evaluation reduces gas costs in several ways:
Deferred Storage Updates: Instead of updating storage (which is expensive in Ethereum) every time an order is partially filled or a position changes, updates are batched and performed only when necessary.
Calculation vs. Storage: The protocol uses real-time calculations instead of storage updates whenever possible. Reading from storage is much cheaper than writing to it.
Batched Operations: Multiple changes can be combined into a single storage update when a user takes an action like withdrawing funds.
Reduced Contract Calls: By handling multiple state changes in a single operation, the number of contract calls is reduced.
Optimized Auto-Roll: The auto-roll process would be prohibitively expensive without lazy evaluation, as it would require updating every position at maturity.
The CleanUp process is triggered by specific user actions:
Order Execution: When a user places a new order that matches with existing orders
Collateral Withdrawals: When a user withdraws collateral from the system
Position Modifications: When a user modifies their position (e.g., adding more funds)
Token Minting/Burning: When a user mints or burns ZC tokens
Manual Settlement: When a user manually settles a position at maturity
The CleanUp process is designed to occur during operations that already require storage updates, minimizing additional gas costs.
Lazy Evaluation is designed to be transparent to users:
Real-Time Information: Users always see the current state of their positions, calculated in real-time
Lower Transaction Costs: Users pay significantly lower gas fees for transactions
Faster Transactions: With fewer storage operations, transactions confirm more quickly
Seamless Auto-Roll: Users don't need to manually roll over positions at maturity
No Action Required: Users don't need to take any special actions to benefit from lazy evaluation
The system handles all the complexity behind the scenes, providing users with an intuitive experience while optimizing for gas efficiency.
No, Lazy Evaluation is designed to maintain complete consistency:
Deterministic Calculations: All calculations are deterministic and will produce the same result regardless of when they're performed
Smart Contract Guarantees: The smart contract ensures that lazy calculations always reflect the true state
Eventual Consistency: While updates may be deferred, the system will always reach a consistent state
Validation Checks: The protocol includes validation checks to ensure that lazy evaluation doesn't introduce inconsistencies
Formal Verification: The lazy evaluation mechanism has been formally verified to ensure correctness
The protocol prioritizes both efficiency and correctness, ensuring that lazy evaluation never compromises the integrity of the system.
The Red-Black Tree and Lazy Evaluation work together to optimize the orderbook:
Efficient Order Management: The Red-Black Tree provides O(log n) operations for order insertion and deletion
Unlink Operation: When an order is filled, it's "unlinked" from the tree rather than immediately removed
Deferred Cleanup: The actual removal of unlinked nodes happens during the CleanUp process
Optimized Traversal: When searching the tree, unlinked nodes are skipped, maintaining efficient operations
Complementary Optimizations: Both mechanisms work together to minimize gas costs while maintaining performance
This combination of data structures and evaluation strategies is what enables the protocol to achieve its high efficiency.
