Connection Commands

This section covers essential commands for connecting to and managing ClickHouse Cloud connections.

Connection Information

Check Current Connection

SELECT currentUser() AS current_user,
       currentDatabase() AS current_database,
       currentQueryId() AS query_id;

View Connection Settings

SELECT name, value
FROM system.settings
WHERE name LIKE '%connection%'
ORDER BY name;

Session Management

View Active Sessions

SELECT user,
       client_hostname,
       client_name,
       client_version,
       query_start_time,
       query
FROM system.processes
ORDER BY query_start_time DESC;

Kill a Specific Query

KILL QUERY WHERE query_id = 'query-id-here';

Connection Pool Information

Check Connection Pool Status

SELECT *
FROM system.metrics
WHERE metric LIKE '%Connection%';

Security and Authentication

View User Privileges

SHOW GRANTS FOR CURRENT USER;

Check Access Rights

SELECT * FROM system.grants;

Troubleshooting Tips

Common Connection Issues

Connection Timeout

-- Check network timeouts
SELECT name, value
FROM system.settings
WHERE name LIKE '%timeout%';

Connection Limits

-- Check max connections
SELECT *
FROM system.metrics
WHERE metric = 'TCPConnection';

Best Practices

Always use secure connections (SSL/TLS) in production
Set appropriate timeouts for your use case
Monitor connection pools for potential issues
Use connection pooling when appropriate

Connection String Examples

# Basic connection string
clickhouse-client --host=<host> --port=9440 --secure --user=<user> --password=<password>

# Connection with specific database
clickhouse-client --host=<host> --port=9440 --secure --database=<database> --user=<user> --password=<password>

Health Checks

Basic Health Check Query

SELECT 1;

Comprehensive Health Check

SELECT
    currentUser() AS user,
    currentDatabase() AS database,
    version() AS version,
    uptime() AS uptime_seconds,
    timezone() AS timezone;