gas-optimization skill

---
name: aptos-gas-optimization
description: Aptos gas optimization expert for Move smart contracts. Covers storage costs, execution efficiency, inline functions, aggregators for parallel execution, Table vs SmartTable vs vector tradeoffs, event optimization, struct packing, and gas profiling tools.
allowed-tools: Read, Write, Edit, Grep, Glob, Bash
model: sonnet
license: MIT
metadata:
  author: raintree
  version: "1.0"
---

# Aptos Gas & Performance Optimization Expert

Expert on optimizing gas costs and performance for Aptos Move smart contracts.

## Triggers

- gas optimization, gas cost, gas fees
- performance tuning, execution efficiency
- storage fees, storage optimization
- inline functions, aggregator
- parallel execution, throughput
- Table vs vector, SmartTable
- gas profiling, benchmarking

## Gas Model Overview

```
Total Gas Cost = Execution Gas + Storage Gas + IO Gas

Gas Fee (APT) = Gas Units x Gas Unit Price
1 APT = 100,000,000 octas
```

## Data Structure Costs

| Structure | Read | Write | Best For |
|-----------|------|-------|----------|
| vector | O(n) | O(n) | Small lists (<1000) |
| SimpleMap | O(n) | O(n) | Small maps (<1000) |
| Table | O(1) | O(1) | Large maps |
| SmartTable | O(1) | O(1) | Very large maps (100k+) |
| Aggregator | O(1) | O(1) | **Parallel counters** |

## Key Optimizations

### 1. Use Aggregators for Global Counters

```move
use aptos_framework::aggregator_v2::{Self, Aggregator};

struct Stats has key {
    total_users: Aggregator<u64>  // Concurrent-safe!
}

public fun increment() acquires Stats {
    let stats = borrow_global_mut<Stats>(@protocol);
    aggregator_v2::add(&mut stats.total_users, 1);
    // Multiple txns can do this in parallel!
}
```

### 2. Inline Small Functions

```move
inline fun min(a: u64, b: u64): u64 {
    if (a < b) a else b
}
```

### 3. Cache Loop Lengths

```move
// Bad: calls length() every iteration
while (i < vector::length(v)) { ... }

// Good: cache length
let len = vector::length(v);
while (i < len) { ... }
```

### 4. Use Event V2 (Cheaper)

```move
#[event]
struct TransferEvent has drop, store {
    from: address,
    to: address,
    amount: u64,
}

event::emit(TransferEvent { from, to, amount });
```

### 5. Pack Struct Fields

```move
// Bad: 8 bytes wasted on padding
struct Data { flag1: bool, value1: u64, flag2: bool, value2: u64 }

// Good: group bools together
struct Data { flag1: bool, flag2: bool, value1: u64, value2: u64 }

// Best: pack into bitmap
struct Data { flags: u8, value1: u64, value2: u64 }
```

### 6. Use Table/SmartTable for Large Data

```move
// Bad for large datasets
struct Registry { users: vector<User> }

// Good for large datasets
struct Registry { users: Table<address, User> }

// Best for very large datasets (100k+)
struct Registry { users: SmartTable<address, User> }
```

### 7. Batch Operations

```move
// Single transaction for multiple transfers
public entry fun batch_transfer(
    sender: &signer,
    recipients: vector<address>,
    amounts: vector<u64>
) { ... }
```

### 8. Early Returns

```move
// Check cheapest conditions first
if (amount == 0) return;
if (amount >= MAX) return;
if (!is_valid(user)) return;
// Then do expensive work
```

## Gas Profiling

```bash
# Run tests with gas profiling
aptos move test --gas

# Simulate transaction
aptos move run --function-id 0x1::module::func --profile gas
```

## Checklist Before Mainnet

- [ ] Use aggregators for global counters
- [ ] Inline small helper functions
- [ ] Use Event V2 for all events
- [ ] Use Table/SmartTable for large datasets
- [ ] Pack struct fields efficiently
- [ ] Cache loop lengths
- [ ] Batch operations where possible
- [ ] Early returns for validation
- [ ] Profile with --gas flag