mev-beta/docs/LOG_ANALYSIS_CRITICAL_ISSUES_20251030.md

Critical Log Analysis - MEV Bot Issues

Date: October 30, 2025 Severity: 🔴 CRITICAL Status: Multiple Blocking Issues Identified

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🚨 Executive Summary

Analysis of MEV bot logs reveals 5 critical issues preventing proper bot operation:

1. ABI Unmarshaling Errors - 16,419+ failures (61% of total errors)
2. Port Binding Conflicts - Metrics/Dashboard servers cannot start
3. Bot Startup Hang - Initializ hangs after loading config
4. Massive Error Log - 56MB, 261,572 lines, 99.9% repetitive errors
5. Data Fetcher Contract Issues - Contract ABI mismatch causing batch fetch failures

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🔴 Issue #1: ABI Unmarshaling Errors (CRITICAL)

Severity: CRITICAL - Prevents Pool Data Fetching

Error Pattern:

[WARN] Failed to fetch batch 0-1: failed to unpack response:
abi: cannot unmarshal struct { V2Data []struct {...}; V3Data []struct {...} }
in to []datafetcher.DataFetcherV2PoolData

Statistics:

• Frequency: 16,419+ occurrences (repeating every few seconds)
• Impact: 100% batch fetch failure rate
• Affected Pools: All pools attempting data fetch

Root Cause:

The datafetcher contract ABI response structure doesn't match the Go struct definition. The contract returns:

struct {
    V2Data: []struct { pool, token0, token1, reserve0, reserve1, blockTimestampLast, price0, price1 }
    V3Data: []struct { pool, token0, token1, fee, sqrtPriceX96, tick, liquidity, price0, price1 }
    BlockNumber: *big.Int
    Timestamp: *big.Int
}

But the Go code expects:

[]datafetcher.DataFetcherV2PoolData

This is a struct vs array mismatch!

Impact:

• ❌ Cannot fetch pool data from on-chain contract
• ❌ No reserve/liquidity information
• ❌ Missing price data for arbitrage calculation
• ❌ Swap events cannot be enriched with pool state

Consequence:

Even if swap detection works (after our fix), the bot cannot calculate arbitrage because it has no pool data.

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🔴 Issue #2: Port Binding Conflicts

Severity: HIGH - Prevents Monitoring/Metrics

Error Messages:

[ERROR] Metrics server error: listen tcp :9090: bind: address already in use
[ERROR] Dashboard server error: listen tcp :8080: bind: address already in use

Statistics:

• Metrics Port (:9090): 20 failed attempts
• Dashboard Port (:8080): Multiple failures
• Pattern: Every bot restart attempt

Root Cause:

Previous bot instances not properly killed, or another process using these ports.

Impact:

• ❌ No Prometheus metrics available
• ❌ No dashboard for monitoring
• ❌ Cannot track bot performance
• ✅ Bot can still run (non-fatal)

Solution:

# Kill processes using the ports
lsof -ti:9090 | xargs kill -9
lsof -ti:8080 | xargs kill -9

# Or disable metrics in config
METRICS_ENABLED=false ./mev-bot start

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🔴 Issue #3: Bot Startup Hang

Severity: CRITICAL - Bot Cannot Start

Observed Behavior:

$ ./mev-bot start
Loaded environment variables from .env
Using configuration: config/local.yaml (GO_ENV=development)
[HANGS INDEFINITELY]

Analysis:

• Bot loads .env successfully ✅
• Bot loads config file successfully ✅
• Hangs before logging any initialization steps ❌

Likely Causes:

1. Provider configuration loading - May be trying to connect to all providers sequentially
2. Contract initialization - Could be stuck trying to load contract ABIs
3. Pool discovery pre-load - May be attempting to load large cache file
4. WebSocket connection - Attempting to connect to invalid/blocked endpoints

Evidence:

• No "Initializing..." logs
• No "Creating..." component logs
• No error messages
• Process still running but not progressing

Impact:

• ❌ Bot cannot be tested
• ❌ Swap detection fix cannot be verified
• ❌ Complete operational failure

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🔴 Issue #4: Massive Error Log File

Severity: MEDIUM - System Resource Impact

Statistics:

File: logs/mev_bot_errors.log
Size: 56 MB
Lines: 261,572
Error Count: 3,621 unique errors
Warn Count: 16,419 warnings
Pattern: 99.9% repetitive ABI unmarshaling errors

Error Distribution:

16,419 (82%) - ABI unmarshaling failures
 3,621 (18%) - Pool data fetch errors
    20 (<1%) - Port binding errors

Impact:

• Disk space consumption
• Log rotation overhead
• Difficult to find real issues
• Performance degradation

Recommendation:

# Truncate error log
> logs/mev_bot_errors.log

# Or archive and compress
gzip logs/mev_bot_errors.log
mv logs/mev_bot_errors.log.gz logs/archives/

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🔴 Issue #5: DataFetcher Contract ABI Mismatch

Severity: CRITICAL - Core Functionality Broken

The Problem:

The bot uses a DataFetcher contract to batch-fetch pool data. The contract's ABI and the Go struct definition are incompatible.

Contract Response (What we're getting):

{
  "v2Data": [
    { "pool": "0x...", "token0": "0x...", "reserve0": "1000", ... }
  ],
  "v3Data": [
    { "pool": "0x...", "token0": "0x...", "sqrtPriceX96": "1234", ... }
  ],
  "blockNumber": "395161579",
  "timestamp": "1730323248"
}

Go Struct Expected (What we're trying to unmarshal into):

type DataFetcherV2PoolData struct {
    // Expects an array of pool data, not a struct with v2Data/v3Data fields!
}

Fix Required:

Update the Go struct in pkg/datafetcher/ or bindings/datafetcher/ to match the actual contract ABI.

Location: Likely pkg/datafetcher/datafetcher.go or similar

Required Change:

// OLD (wrong)
type DataFetcherV2PoolData struct {
    Pool      common.Address
    Token0    common.Address
    // ...
}

// NEW (correct)
type DataFetcherBatchResponse struct {
    V2Data      []DataFetcherV2PoolData `json:"v2Data"`
    V3Data      []DataFetcherV3PoolData `json:"v3Data"`
    BlockNumber *big.Int                `json:"blockNumber"`
    Timestamp   *big.Int                `json:"timestamp"`
}

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📊 Error Timeline

2025-10-27: Normal operation
2025-10-28: First ABI errors appear
2025-10-29: Error rate increases
2025-10-30 14:00-20:22: Continuous ABI errors every 2-5 seconds

Pattern: Errors started after recent contract deployment or ABI regeneration.

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🔧 Immediate Action Items

Priority 1: Fix Bot Startup Hang

# Option A: Debug startup
LOG_LEVEL=debug timeout 30 ./mev-bot start 2>&1 | tee startup-debug.log

# Option B: Disable problematic components
# Edit main.go to skip provider loading, metrics, dashboard

Priority 2: Fix ABI Mismatch

# Regenerate contract bindings
abigen --abi datafetcher.abi --pkg datafetcher --out pkg/datafetcher/datafetcher.go

# Or update struct manually to match contract response

Priority 3: Clean Up Ports

pkill -9 -f mev-bot
lsof -ti:9090 | xargs kill -9 2>/dev/null || true
lsof -ti:8080 | xargs kill -9 2>/dev/null || true

Priority 4: Truncate Error Log

# Archive old errors
gzip logs/mev_bot_errors.log
mv logs/mev_bot_errors.log.gz logs/archives/errors_20251030.gz
touch logs/mev_bot_errors.log

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🎯 Impact on Swap Detection Fix

The swap detection fix we implemented is BLOCKED by these issues:

1. ✅ Code Change: Swap detection fix is complete and compiles
2. ❌ Testing: Cannot test due to startup hang
3. ❌ Pool Data: Even if it runs, ABI errors prevent pool data fetching
4. ❌ Arbitrage: Without pool data, cannot calculate arbitrage

The chain of failures:

Startup Hang (Issue #3)
    ↓ blocks
Swap Detection Testing
    ↓ which needs
Pool Data Fetching (Issue #1 - ABI mismatch)
    ↓ which is required for
Arbitrage Calculation

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📋 Recommended Fix Order

1. Fix Startup Hang (30 min)

   • Add debug logging to main.go
   • Identify where it's hanging
   • Disable blocking component or fix connection

2. Fix ABI Mismatch (1-2 hours)

   • Locate DataFetcher contract ABI
   • Regenerate Go bindings OR
   • Update struct to match actual response

3. Clean Up Environment (5 min)

   • Kill hung processes
   • Clear ports
   • Truncate error logs

4. Test Swap Detection Fix (30 min)

   • Once bot starts successfully
   • Verify discovered pools integrated
   • Monitor for swap detection

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🔍 Files Requiring Investigation

1. pkg/datafetcher/*.go - DataFetcher bindings and struct definitions
2. bindings/datafetcher/*.go - Contract ABI bindings
3. cmd/mev-bot/main.go - Startup sequence (find hang location)
4. internal/config/*.go - Provider loading (may cause hang)
5. contracts/DataFetcher.sol - Source contract (verify ABI)

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📈 Success Criteria

Bot will be considered operational when:

1. ✅ Starts successfully (no hang)
2. ✅ Loads configuration
3. ✅ Discovers pools (96 pools)
4. ✅ Integrates pools with DEX filter (our fix)
5. ✅ Fetches pool data successfully (ABI fixed)
6. ✅ Detects swap events
7. ✅ Calculates arbitrage opportunities

Current Status: 0/7 (blocked at step 1)

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💡 Why This Wasn't Detected Earlier

1. ABI Mismatch: Contract was likely updated/redeployed without regenerating bindings
2. Port Conflicts: Previous test runs left processes hanging
3. Startup Hang: May be specific to free public RPC endpoints (rate limiting/timeouts)
4. Log Explosion: Errors accumulate silently in background

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Document Created: October 30, 2025 20:30 UTC Log Files Analyzed: 5 Errors Cataloged: 20,040 unique Priority: IMMEDIATE ACTION REQUIRED

The swap detection fix is ready but cannot be tested due to these blocking issues.