# Partner DLQ (Dead Letter Queue) Handling System

## Overview

The Partner DLQ Handling System provides automatic and manual management of failed partner processing tasks. It categorizes failures, automatically retries transient errors, archives non-recoverable tasks, and provides monitoring tools for administrators.

## Architecture

### Components

1. **Partner Sync Worker** (`workers/partner_sync_worker.js`)
   - Primary task processor
   - Sends failed tasks to DLQ after max retries
   - Implements circuit breaker for problematic files

2. **DLQ Handler** (`workers/partner_dlq_handler.js`)
   - Monitors and processes DLQ messages
   - Categorizes errors and makes retry/archive decisions
   - Provides programmatic DLQ management

3. **DLQ Monitor** (`scripts/monitor_partner_dlq.js`)
   - Interactive dashboard for DLQ monitoring
   - Manual operations and statistics

### Message Flow

```mermaid
flowchart TD
    A[Polling Worker<br/>Enqueues Task] --> B[Partner Queue<br/>Main Queue]
    B -->|Processing| C[Sync Worker<br/>Processing]
    B -->|Max Retries<br/>Exceeded| D[Dead Letter Queue<br/>DLQ]
    D --> E[DLQ Handler<br/>Analysis]
    E --> F[Retry<br/>Queue]
    E --> G[Archive<br/>DB]
    E --> H[Manual<br/>Review]
```

## Error Categories

### 1. Transient Errors
- Network timeouts
- Temporary connection issues
- Database connection failures
- **Action**: Auto-retry within 2-hour window

### 2. Validation Errors
- Invalid file format
- Missing required fields
- Data validation failures
- **Action**: Archive immediately, notify admin

### 3. Processing Errors
- Calculation errors
- Parse errors
- Logic errors
- **Action**: Keep for manual review

### 4. Infrastructure Errors
- Database errors
- Filesystem errors
- Transaction failures
- **Action**: Retry with exponential backoff

### 5. Partner API Errors
- API authentication failures
- Rate limiting
- Partner service unavailable
- **Action**: Retry with longer delay

## Configuration

### Environment Variables

```bash
# Queue Configuration
QUEUE_HOST=localhost
QUEUE_PORT=5672
QUEUE_USR=agmuser
QUEUE_PWD=<password>
QUEUE_NAME_PARTNER=partner_tasks  # Base name, auto-prefixes 'dev_' when PRODUCTION=false

# Retry Configuration
PARTNER_MAX_RETRIES=5              # Max retries before DLQ
PARTNER_RETRY_DELAY=10000          # Base retry delay (ms)

# DLQ Configuration
DLQ_CHECK_INTERVAL=300000          # Check DLQ every 5 minutes
MAX_DLQ_AGE_MS=86400000           # Archive after 24 hours
AUTO_RETRY_WINDOW_MS=7200000      # Auto-retry within 2 hours
```

### Worker Constants

```javascript
// Circuit Breaker
MAX_FILE_ATTEMPTS = 10 (dev) / 3 (prod)
FILE_BLOCK_DURATION = 5 min (dev) / 1 hour (prod)

// Timeouts
PROCESSING_TIMEOUT_MS = 90 minutes
TASK_TIMEOUT_MS = 90 minutes
CLEANUP_INTERVAL_MS = 15 minutes
```

## Usage

### 1. Start DLQ Handler (Automatic Mode)

```bash
# Run as background service
node workers/partner_dlq_handler.js monitor &

# Or with PM2
pm2 start workers/partner_dlq_handler.js --name partner-dlq-handler -- monitor
```

### 2. Manual DLQ Operations

```bash
# Show DLQ statistics
node workers/partner_dlq_handler.js stats

# Process DLQ messages once
node workers/partner_dlq_handler.js process
```

### 3. Interactive Dashboard

```bash
# Launch monitoring dashboard
node scripts/monitor_partner_dlq.js
```

Dashboard commands:
- `r` - Refresh dashboard
- `p` - Process DLQ now
- `s` - Show detailed statistics
- `c` - Clear archived tasks (> 7 days old)
- `q` - Quit

## Monitoring

### DLQ Statistics

```javascript
{
  messageCount: 5,        // Messages in DLQ
  consumerCount: 0,       // Active consumers
  queueName: 'partner_tasks_failed'
}
```

### Tracker Statistics

```javascript
{
  failed: 12,            // Failed tasks
  processing: 3,         // Currently processing
  downloaded: 8,         // Downloaded, waiting
  processed: 245,        // Successfully processed
  archived: 7            // Archived from DLQ
}
```

## Queue-Native Operations

### Retry Operations (Recommended - Direct RabbitMQ)

```bash
# Retry all messages in queue
curl -X POST http://localhost:3000/api/dlq/partner_tasks/retryAll \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"maxMessages": 50}'

# Retry by position range (0-based index)
curl -X POST http://localhost:3000/api/dlq/partner_tasks/retryByPosition \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"startPosition": 0, "endPosition": 10}'

# Retry by header match
curl -X POST http://localhost:3000/api/dlq/partner_tasks/retryByHeader \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"headerKey": "x-retry-count", "headerValue": "1"}'
```

**Benefits**: 
- No MongoDB coupling
- Preserves original message content
- Supports multiple queue types
- Direct RabbitMQ operations

### Legacy Manual Recovery (Programmatic)

For advanced debugging scenarios only:

```javascript
const handler = new PartnerDLQHandler();
await handler.start();

// Get message from DLQ
const msg = await handler.channel.get('partner_tasks_failed');

// Retry it programmatically
await handler.retryMessage(msg, JSON.parse(msg.content));
```

### Clear Stuck Tasks

```bash
# Reset stuck processing tasks
mongo mongodb://localhost:27017/agmission << EOF
use agmission
db.partnerlogtrackers.updateMany(
  { 
    status: 'processing',
    processingStartedAt: { \$lt: new Date(Date.now() - 90*60*1000) }
  },
  { 
    \$set: { 
      status: 'failed',
      errorMessage: 'Manually reset - stuck processing'
    }
  }
)
EOF
```

### Purge DLQ

```bash
# WARNING: This deletes all DLQ messages
rabbitmqadmin purge queue name=partner_tasks_failed
```

## Troubleshooting

### High DLQ Message Count

1. Check error patterns:
   ```bash
   node scripts/monitor_partner_dlq.js
   # Press 's' for detailed stats
   ```

2. Identify root cause:
   - **Validation errors**: Fix data source or add validation
   - **Transient errors**: Check infrastructure (network, DB, partner API)
   - **Processing errors**: Review logs, fix code bugs

3. Take action:
   - Fix root cause
   - Process DLQ: `node workers/partner_dlq_handler.js process`
   - Monitor results

### Memory Issues

1. Check worker memory:
   ```bash
   ps aux | grep partner_sync_worker
   ```

2. If high memory usage:
   - Reduce `batchSize` in processor options
   - Increase `PROCESSING_TIMEOUT_MS`
   - Enable garbage collection: `node --expose-gc --max-old-space-size=2048`

### Circuit Breaker Blocking Files

1. Check blocked files:
   ```javascript
   // In partner_sync_worker.js, add logging:
   setInterval(() => {
     console.log('Blocked files:', Array.from(problematicFiles.keys()));
   }, 60000);
   ```

2. Reset circuit breaker:
   - Restart worker (circuit breaker is in-memory)
   - Or adjust thresholds for development

## Best Practices

### 1. Monitoring
- Set up alerts for high DLQ message count (> 50)
- Monitor DLQ age (messages > 1 hour need attention)
- Track processing success rate

### 2. Retry Strategy
- Use exponential backoff for retries
- Categorize errors properly
- Don't retry validation errors

### 3. Circuit Breaker
- Use lenient settings in development
- Use strict settings in production
- Monitor blocked files regularly

### 4. Database Cleanup
- Archive old failed tasks (> 30 days)
- Keep DLQ archived tasks for audit (7 days)
- Regularly check for stuck processing tasks

## API Reference

### PartnerDLQHandler

```javascript
const handler = new PartnerDLQHandler();

// Start handler
await handler.start();

// Process DLQ
await handler.processDLQ();

// Get statistics
const stats = await handler.getStatistics();

// Stop handler
await handler.stop();
```

### Error Categories

```javascript
ERROR_CATEGORIES = {
  TRANSIENT: 'transient',
  VALIDATION: 'validation',
  PROCESSING: 'processing',
  INFRASTRUCTURE: 'infrastructure',
  PARTNER_API: 'partner_api',
  UNKNOWN: 'unknown'
}
```

## Future Enhancements

1. **Email/Slack Notifications**
   - Alert admins on critical failures
   - Daily DLQ summary reports

2. **Advanced Analytics**
   - Failure trend analysis
   - Automatic root cause detection
   - Performance metrics

3. **Automatic Recovery**
   - Smart retry scheduling
   - Self-healing for known issues
   - Predictive failure prevention

4. **Web Dashboard**
   - Real-time DLQ visualization
   - One-click retry/archive
   - Historical analysis

## Related Documentation

- [Partner Integration Architecture](./PARTNER_INTEGRATION_ARCHITECTURE.md)
- [SatLoc Implementation Summary](./SATLOC_IMPLEMENTATION_SUMMARY.md)
- [Worker Responsibilities Update](./WORKER_RESPONSIBILITIES_UPDATE.md)