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gas-optimization.md

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Gas Optimization Report

This document records the implemented gas/cost-efficiency pass for the RemitWise Soroban contracts and maps to the acceptance criteria described in AGENTS.md (without modifying AGENTS.md itself).

Scope

Benchmarked/optimized contracts in this pass:

  • remittance_split
  • savings_goals
  • bill_payments
  • insurance
  • family_wallet

reporting and data_migration were reviewed, but no gas benchmark harness exists in this repository for them yet.

Implemented Optimizations

Storage / Data Access

  • bill_payments: added cached per-owner unpaid totals (UNPD_TOT) and maintained it on create_bill, pay_bill, cancel_bill, and batch_pay_bills
  • insurance: added cached per-owner active premium totals (PRM_TOT) and maintained it on create_policy and deactivate_policy
  • savings_goals: added owner -> goal-id index (OWN_GOAL) and used a hybrid read path in get_all_goals(owner):
    • full-scan fast path when the owner owns all goals (avoids extra lookups)
    • index lookup path when the owner owns a subset

Computation / Hot Paths

  • remittance_split:
    • removed duplicate arithmetic in calculate_split
    • introduced internal split calculator with optional event emission
    • distribute_usdc now uses the non-event internal path to avoid redundant event work and temporary vector allocation
    • reduced redundant Env/Address clones in nonce helpers
  • family_wallet:
    • removed redundant signers.clone() in configure_multisig
    • reused signers.len() result during threshold validation

Code Size / Unused Code Cleanup

  • Removed dead, uncompiled file bill_payments/src/schedule.rs (it was not linked into the crate and used #![allow(dead_code)])
  • Removed stale commented-out mod schedule scaffolding from bill_payments/src/lib.rs
  • Verified all optimized contracts compile cleanly with cargo check (no compiler warnings surfaced in this pass)

Compiler Optimizations (Verified)

The workspace root Cargo.toml already includes release profile settings suitable for Soroban contract size/runtime cost efficiency:

  • opt-level = "z" (optimize for size)
  • lto = true
  • codegen-units = 1
  • panic = "abort"
  • strip = "symbols"
  • debug = 0
  • debug-assertions = false

These settings were retained and verified during release WASM builds.

Gas Benchmarks (Before vs After)

Benchmark commands:

RUST_TEST_THREADS=1 cargo test -p remittance_split --test gas_bench -- --nocapture
RUST_TEST_THREADS=1 cargo test -p savings_goals --test gas_bench -- --nocapture
RUST_TEST_THREADS=1 cargo test -p bill_payments --test gas_bench -- --nocapture
RUST_TEST_THREADS=1 cargo test -p insurance --test gas_bench -- --nocapture
RUST_TEST_THREADS=1 cargo test -p family_wallet --test gas_bench -- --nocapture
Contract Method CPU Before CPU After CPU Delta Mem Before Mem After Mem Delta
remittance_split distribute_usdc 656,918 638,399 -18,519 (-2.82%) 86,323 84,687 -1,636 (-1.90%)
savings_goals get_all_goals 2,661,552 2,642,861 -18,691 (-0.70%) 480,721 495,233 +14,512 (+3.02%)
bill_payments get_total_unpaid 1,077,221 1,000,587 -76,634 (-7.11%) 235,460 236,260 +800 (+0.34%)
insurance get_total_monthly_premium 2,373,104 2,213,216 -159,888 (-6.74%) 427,575 428,373 +798 (+0.19%)
family_wallet configure_multisig 307,374 307,374 0 (0.00%) 60,934 60,934 0 (0.00%)

Aggregate across benchmarked methods:

  • CPU: 7,076,169 -> 6,802,437 (-273,732, -3.87%)
  • Memory: 1,291,013 -> 1,305,487 (+14,474, +1.12%)

Release WASM Artifact Sizes (Current)

Built with:

cargo build --release --target wasm32-unknown-unknown \
  -p remittance_split -p savings_goals -p bill_payments -p insurance -p family_wallet

Current artifact sizes:

  • target/wasm32-unknown-unknown/release/remittance_split.wasm: 48,297 bytes
  • target/wasm32-unknown-unknown/release/savings_goals.wasm: 55,527 bytes
  • target/wasm32-unknown-unknown/release/bill_payments.wasm: 39,523 bytes
  • target/wasm32-unknown-unknown/release/insurance.wasm: 42,057 bytes
  • target/wasm32-unknown-unknown/release/family_wallet.wasm: 63,296 bytes

Validation

Commands executed during this pass:

cargo check -p remittance_split -p savings_goals -p bill_payments -p insurance -p family_wallet

cargo test -p remittance_split --test gas_bench -- --nocapture
cargo test -p savings_goals --test gas_bench -- --nocapture
cargo test -p bill_payments --test gas_bench -- --nocapture
cargo test -p insurance --test gas_bench -- --nocapture
cargo test -p family_wallet --test gas_bench -- --nocapture

cargo test -p remittance_split -p savings_goals -p bill_payments -p insurance -p family_wallet

Notes / Tradeoffs

  • Cached aggregates improve read-path CPU for common totals but increase write work on state transitions.
  • savings_goals indexing is deliberately hybrid to avoid regressing the single-owner-worst-case benchmark while improving subset-owner reads in multi-user scenarios.
  • Snapshot fixture files under */test_snapshots/ changed because contract storage/state outputs changed after the new caches/indexes were introduced.