Troubleshooting

Common issues and solutions when using Sling.

Connection Issues

Connection Refused

Error: failed to connect to database

Solutions:

1. Check host/port accessibility: telnet host port
2. Verify firewall rules allow traffic
3. Confirm database is running
4. Check for VPN requirements

Authentication Failed

Error: authentication failed for user

Solutions:

1. Verify username and password
2. Check user has required permissions
3. Review database authentication logs
4. Confirm SSL/TLS settings match

SSL/TLS Errors

Error: SSL certificate problem

Solutions:

1. For testing: add sslmode=disable (not for production)
2. Verify certificate validity
3. Check SSL configuration matches server
4. Ensure CA certificates are available

Test Connection

# Via CLI
sling conns test MY_CONN --debug

# Via MCP
{"action": "test", "input": {"connection": "MY_CONN", "debug": true}}

Replication Issues

Table Not Found

Error: table "schema.table" does not exist

Solutions:

1. Discover available tables:

   sling conns discover MY_CONN --pattern "schema.*"
   

2. Check case sensitivity (some DBs are case-sensitive)
3. Verify user has SELECT permission

Type Conversion Errors

Error: cannot convert value to target type

Solutions:

1. Add explicit type casting:

   columns:
     problematic_col: string
   transforms:
     - problematic_col: 'cast(value, "integer")'
   

2. Handle nulls:

   transforms:
     - amount: 'coalesce(value, 0)'
   

3. Clean data:

   transforms:
     - value: 'replace(value, "[^0-9]", "")'
   

Primary Key Violations

Error: duplicate key value violates unique constraint

Solutions:

1. Verify primary key is correct
2. Check for duplicate source data
3. Use mode: full-refresh to replace data
4. Deduplicate in source query

Memory Issues

Error: out of memory processing large dataset

Solutions:

1. Reduce batch size:

   env:
     SLING_BATCH_SIZE: 5000
   

2. Enable chunking:

   source_options:
     chunk_size: 6h
   

3. Use file splitting:

   target_options:
     file_max_rows: 100000
   

4. Reduce parallelism:

   env:
     SLING_THREADS: 2
   

Performance Issues

Slow Performance

Database sources:

1. Increase threads:

   env:
     SLING_THREADS: 10
   

2. Enable bulk loading:

   target_options:
     use_bulk: true
   

3. Use incremental mode instead of full-refresh

File sources:

1. Use parallel file processing:

   env:
     SLING_THREADS: 20
   

2. Compress output files:

   target_options:
     compression: snappy
   

High Memory Usage

1. Stream large tables with chunking
2. Reduce batch sizes
3. Process fewer concurrent streams

Debug Options

Enable Debug Logging

# CLI
sling run -r replication.yaml --debug

# MCP
{"action": "run", "input": {"file_path": "...", "env": {"DEBUG": "true"}}}

Enable Trace Logging

sling run -r replication.yaml --trace

Validate Configuration

# Parse only (no execution)
sling run -r replication.yaml --parse

# Or via MCP
{"action": "parse", "input": {"file_path": "replication.yaml"}}

API Spec Issues

Rate Limiting

Error: 429 Too Many Requests

Solutions:

1. Reduce request rate:

   defaults:
     request:
       rate: 1  # Requests per second
   

2. Configure retry:

   response:
     rules:
       - action: retry
         condition: response.status == 429
         max_attempts: 5
         backoff: exponential
   

Authentication Errors

Error: 401 Unauthorized

Solutions:

1. Verify API credentials
2. Check token expiration
3. Confirm required scopes
4. Test with curl first

Pagination Loops

API keeps returning same data.

Solutions:

1. Check pagination stop_condition
2. Verify cursor/offset updates correctly
3. Debug with limit:

   response:
     records:
       limit: 100  # Stop after 100 records
   

File Issues

File Not Found

Error: file not found

Solutions:

1. Check file path exists
2. Verify connection configuration
3. Confirm user has read access
4. Check for typos in path

Encoding Errors

Error: invalid character encoding

Solutions:

1. Specify encoding:

   source_options:
     encoding: utf8  # or latin1, windows1252
   

2. Clean source data

Format Detection Failed

Solutions:

1. Explicitly set format:

   source_options:
     format: csv
     header: true
     delimiter: ','
   

Error Recovery

Resume Failed Replications

Sling tracks progress automatically. Re-run to resume.

Retry Configuration

env:
  SLING_RETRIES: 3
  SLING_RETRY_DELAY: 60s

Run Specific Streams

# CLI
sling run -r replication.yaml --select "failed_table"

# MCP
{"action": "run", "input": {"file_path": "...", "select_streams": ["failed_table"]}}

Getting Help

1. Debug output: Run with --debug or --trace
2. Parse first: Validate config before running
3. Test connections: Always test before replicating
4. Check logs: Review database/API logs

Support Channels

• Docs: https://docs.slingdata.io
• Discord: https://discord.gg/q5xtaSNDvp
• GitHub Issues: https://github.com/slingdata-io/sling-cli/issues
• Email: support@slingdata.io