Troubleshooting Common Issues

Having problems with ClickHouse? Find the solutions to common issues here.

Performance and Errors

Queries running slowly, timeouts, or getting specific error messages like "Memory limit exceeded" or "Connection refused."

Show performance and error solutions

Query Performance

• Find which queries are using the most resources
• Complete query optimization guide
• Optimize JOIN operations
• Run diagnostic queries to find bottlenecks

Data Insertion Performance

• Speed up data insertion
• Set up asynchronous inserts

Advanced Analysis Tools

• Profile with LLVM XRay
• Check what processes are running
• Monitor system performance

Error Messages

• "Memory limit exceeded" → Debug memory limit errors
• "Connection refused" → Fix connection problems
• "Login failures" → Set up users, roles, and permissions
• "SSL certificate errors" → Fix certificate problems
• "Table/database errors" → Database creation guide | Table UUID problems
• "Network timeouts" → Network troubleshooting
• Other issues → Track errors across your cluster

Memory and Resources

High memory usage, out-of-memory crashes, or need help sizing your ClickHouse deployment.

Show memory solutions

Memory debugging and monitoring:

• Identify what's using memory
• Check current memory usage
• Memory allocation profiling
• Analyze memory usage patterns

Memory configuration:

• Configure memory limits
• Server memory settings
• Session memory settings

Scaling and sizing:

• Right-size your service
• Configure automatic scaling

Connections and Authentication

Can't connect to ClickHouse, authentication failures, SSL certificate errors, or client setup issues.

Show connection solutions

Basic Connection Issues

• Fix HTTP interface issues
• Handle SSL certificate problems
• User authentication setup

Client Interfaces

• Native ClickHouse clients
• MySQL interface problems
• PostgreSQL interface issues
• gRPC interface configuration
• SSH interface setup

Network and Data

• Network security settings
• Data format parsing issues

Setup and Configuration

Initial installation, server configuration, database creation, data ingestion issues, or replication setup.

Show setup and configuration solutions

Initial Setup

• Configure server settings
• Set up security and access control
• Configure hardware properly

Database Management

• Create and manage databases
• Choose the right table engine

Data Operations

• Optimize bulk data insertion
• Handle data format problems
• Set up streaming data pipelines
• Improve S3 integration performance

Advanced Configuration

• Set up data replication
• Configure distributed tables

• Set up backup and recovery
• Configure monitoring

Still Need Help?

If you can't find a solution:

1. Check system tables - Run SELECT * FROM system.processes and SELECT * FROM system.query_log ORDER BY event_time DESC LIMIT 10
2. Review server logs - Look for error messages in your ClickHouse logs
3. Ask the community - GitHub Discussions
4. Get professional support - ClickHouse Cloud support