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Co-authored-by: Cursor <cursoragent@cursor.com>
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docs/specs/mempool/fee-oracle.md
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docs/specs/mempool/fee-oracle.md
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# Fee Oracle Specification
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## Overview
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This document specifies the fee estimation service that calculates and predicts transaction fees based on historical data and current mempool conditions.
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## Architecture
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```mermaid
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flowchart TB
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subgraph Data[Data Sources]
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Blocks[Recent Blocks]
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Mempool[Current Mempool]
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History[Historical Data]
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end
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subgraph Analysis[Analysis]
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Percentile[Percentile Calculator]
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Prediction[Prediction Model]
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Adjust[Market Adjuster]
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end
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subgraph Output[Output]
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Estimates[Fee Estimates]
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API[API Endpoint]
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Cache[Cache]
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end
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Blocks --> Percentile
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Mempool --> Percentile
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History --> Prediction
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Percentile --> Adjust
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Prediction --> Adjust
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Adjust --> Estimates
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Estimates --> API
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Estimates --> Cache
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```
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## Fee Calculation Methods
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### Method 1: Percentile-Based (Primary)
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**Algorithm**:
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1. Collect gas prices from recent N blocks (e.g., 100 blocks)
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2. Calculate percentiles: 25th, 50th, 75th, 95th
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3. Use percentiles as fee estimates
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**Percentile Mapping**:
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- Slow: 25th percentile
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- Standard: 50th percentile (median)
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- Fast: 75th percentile
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- Urgent: 95th percentile
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**Update Frequency**: Every new block
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### Method 2: Mempool-Based Adjustment
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**Algorithm**:
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1. Start with percentile-based estimates
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2. Analyze current mempool:
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- Average gas price of pending transactions
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- Pending transaction count
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- Mempool pressure (pending / recent block capacity)
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3. Adjust estimates based on mempool conditions
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**Adjustment Factors**:
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- High mempool pressure → Increase estimates
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- Low mempool pressure → Decrease estimates
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- Recent confirmed gas prices → Weight recent data more
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### Method 3: Time-Based Prediction
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**Algorithm**:
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- Predict fees for different confirmation times
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- Example: "To be confirmed in 1 block, use X gas price"
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- Use historical data to train model
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**Prediction Targets**:
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- 1 block (next block)
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- 3 blocks (within 3 blocks)
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- 10 blocks (within 10 blocks)
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## Fee Estimate Structure
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### Standard Estimates
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```json
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{
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"chain_id": 138,
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"block_number": 12345,
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"estimates": {
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"slow": {
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"gas_price": "20000000000",
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"max_fee_per_gas": "20000000000",
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"max_priority_fee_per_gas": "1000000000",
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"confidence": 0.95,
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"estimated_confirmation_time": "5 minutes"
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},
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"standard": {
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"gas_price": "30000000000",
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"max_fee_per_gas": "30000000000",
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"max_priority_fee_per_gas": "2000000000",
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"confidence": 0.90,
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"estimated_confirmation_time": "2 minutes"
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},
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"fast": {
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"gas_price": "50000000000",
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"max_fee_per_gas": "50000000000",
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"max_priority_fee_per_gas": "3000000000",
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"confidence": 0.85,
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"estimated_confirmation_time": "30 seconds"
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},
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"urgent": {
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"gas_price": "100000000000",
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"max_fee_per_gas": "100000000000",
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"max_priority_fee_per_gas": "5000000000",
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"confidence": 0.80,
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"estimated_confirmation_time": "next block"
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}
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},
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"timestamp": "2024-01-01T00:00:00Z"
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}
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```
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### EIP-1559 Support
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**For EIP-1559 Chains**:
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- Provide `max_fee_per_gas` and `max_priority_fee_per_gas`
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- Calculate base fee prediction
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- Estimate priority fee needed for desired speed
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## Historical Fee Analysis
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### Data Collection
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**Sources**:
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- Recent blocks (last 100-1000 blocks)
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- Historical fee data (time-series database)
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**Metrics Tracked**:
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- Min, max, average gas price per block
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- Percentiles (25th, 50th, 75th, 95th, 99th)
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- Gas price distribution
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- Confirmation time by gas price
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### Analysis Windows
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**Short-term** (Last 10 blocks):
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- Most recent trends
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- Quick response to market changes
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**Medium-term** (Last 100 blocks):
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- Stable baseline
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- Primary estimate source
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**Long-term** (Last 1000 blocks):
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- Historical patterns
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- Anomaly detection
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## Prediction Models
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### Simple Moving Average
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**Algorithm**: Average of recent N blocks
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**Pros**: Simple, fast
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**Cons**: Slow to adapt to changes
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### Weighted Moving Average
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**Algorithm**: Weight recent blocks more heavily
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**Pros**: Faster adaptation
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**Cons**: More volatile
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### Machine Learning Models (Future)
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**Potential Models**:
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- Linear regression
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- Time series forecasting (ARIMA, LSTM)
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- Classification (predict confirmation time)
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**Features**:
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- Historical gas prices
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- Mempool metrics
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- Block time
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- Network activity
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## API Endpoint
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### Get Fee Estimates
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`GET /api/v1/mempool/{chain_id}/fees`
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**Query Parameters**:
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- `block_target` (integer): Target confirmation block (optional)
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**Response**: Fee estimates object (see structure above)
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### Get Fee History
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`GET /api/v1/mempool/{chain_id}/fees/history`
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**Query Parameters**:
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- `period` (string): Time period (1h, 24h, 7d, 30d)
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- `interval` (string): Aggregation interval (1m, 5m, 1h)
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**Response**: Historical fee data with timestamps
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## Caching Strategy
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### Cache Duration
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- **Fee Estimates**: 10 seconds (update every block)
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- **Fee History**: 5 minutes (less frequently updated)
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### Cache Invalidation
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- Invalidate on new block
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- Invalidate on significant mempool changes
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## Performance Considerations
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### Calculation Performance
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**Target**: Calculate estimates in < 100ms
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**Optimization**:
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- Pre-calculate percentiles
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- Cache historical data
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- Use efficient algorithms
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### Update Frequency
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**Block-based**: Update on every new block
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**Time-based**: Update every 10 seconds (fallback)
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## Accuracy Metrics
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### Tracking Accuracy
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**Metrics**:
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- Predicted vs actual confirmation time
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- Predicted vs actual gas price used
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- Estimate accuracy by tier (slow/standard/fast/urgent)
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### Confidence Scores
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**Calculation**:
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- Based on historical accuracy
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- Variance in recent data
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- Mempool stability
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**Display**: Include confidence score in estimates
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## Monitoring
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### Metrics
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- Fee estimate accuracy
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- Update latency
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- Calculation time
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- Cache hit rate
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### Alerts
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- High prediction error (> 50% off)
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- Calculation timeout
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- Cache miss rate spike
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## References
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- Mempool Service: See `mempool-service.md`
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- Time-Series Schema: See `../database/timeseries-schema.md`
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