> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-home-button.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Troubleshooting common issues

> Find solutions to the most common ClickHouse problems including slow queries, memory errors, connection issues, and configuration problems.

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

<h2 id="performance-and-errors">
  Performance and errors
</h2>

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

<Accordion title="Show performance and error solutions">
  <h3 id="query-performance">
    Query performance
  </h3>

  * [Find which queries are using the most resources](/resources/support-center/knowledge-base/performance-optimization/find-expensive-queries)
  * [Complete query optimization guide](/guides/clickhouse/performance-and-monitoring/query-optimization)
  * [Optimize JOIN operations](/concepts/best-practices/minimize-optimize-joins)
  * [Run diagnostic queries to find bottlenecks](/resources/support-center/knowledge-base/queries-sql/useful-queries-for-troubleshooting)

  <br />

  <h3 id="data-insertion-performance">
    Data insertion performance
  </h3>

  * [Speed up data insertion](/concepts/features/operations/insert/bulkinserts)
  * [Set up asynchronous inserts](/concepts/features/operations/insert/asyncinserts)

  <br />

  <h3 id="advanced-analysis-tools">
    Advanced analysis tools
  </h3>

  * [Check what processes are running](/resources/support-center/knowledge-base/monitoring-debugging/which-processes-are-currently-running)
  * [Monitor system performance](/reference/system-tables/processes)

  <br />

  <h3 id="error-messages">
    Error messages
  </h3>

  * **"Memory limit exceeded"** → [Debug memory limit errors](/concepts/features/performance/troubleshoot/debugging-memory-issues)
  * **"Connection refused"** → [Fix connection problems](#connections-and-authentication)
  * **"Login failures"** → [Set up users, roles, and permissions](/concepts/features/security/access-rights)
  * **"SSL certificate errors"** → [Fix certificate problems](/resources/support-center/knowledge-base/troubleshooting/certificate-verify-failed-error)
  * **"Table/database errors"** → [Database creation guide](/reference/statements/create/database) | [Table UUID problems](/reference/engines/database-engines/atomic)
  * **"Network timeouts"** → [Network troubleshooting](/concepts/features/interfaces/http)
  * **Other issues** → [Track errors across your cluster](/reference/system-tables/errors)
</Accordion>

<h2 id="memory-and-resources">
  Memory and resources
</h2>

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

<Accordion title="Show memory solutions">
  <h3 id="memory-debugging-and-monitoring">
    Memory debugging and monitoring:
  </h3>

  * [Identify what's using memory](/concepts/features/performance/troubleshoot/debugging-memory-issues)
  * [Check current memory usage](/reference/system-tables/processes)
  * [Memory allocation profiling](/concepts/features/performance/allocation-profiling)
  * [Analyze memory usage patterns](/reference/system-tables/query_log)

  <br />

  <h3 id="memory-configuration">
    Memory configuration:
  </h3>

  * [Configure memory limits](/concepts/features/configuration/settings/memory-overcommit)
  * [Server memory settings](/reference/settings/server-settings/settings)
  * [Session memory settings](/reference/settings/session-settings)

  <br />

  <h3 id="scaling-and-sizing">
    Scaling and sizing:
  </h3>

  * [Right-size your service](/guides/oss/best-practices/tips)
  * [Configure automatic scaling](/products/cloud/features/autoscaling/overview)
</Accordion>

<h2 id="connections-and-authentication">
  Connections and Authentication
</h2>

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

<Accordion title="Show connection solutions">
  <h3 id="basic-connection-issues">
    Basic Connection issues
  </h3>

  * [Fix HTTP interface issues](/concepts/features/interfaces/http)
  * [Handle SSL certificate problems](/resources/support-center/knowledge-base/troubleshooting/certificate-verify-failed-error)
  * [User authentication setup](/concepts/features/security/access-rights)

  <br />

  <h3 id="client-interfaces">
    Client interfaces
  </h3>

  * [Native ClickHouse clients](/concepts/features/interfaces/native-clients-interfaces-index)
  * [MySQL interface problems](/concepts/features/interfaces/mysql)
  * [PostgreSQL interface issues](/concepts/features/interfaces/postgresql)
  * [gRPC interface configuration](/concepts/features/interfaces/grpc)
  * [SSH interface setup](/concepts/features/interfaces/ssh)

  <br />

  <h3 id="network-and-data">
    Network and data
  </h3>

  * [Network security settings](/reference/settings/server-settings/settings)
  * [Data format parsing issues](/reference/formats)
</Accordion>

<h2 id="setup-and-configuration">
  Setup and configuration
</h2>

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

<Accordion title="Show setup and configuration solutions">
  <h3 id="initial-setup">
    Initial setup
  </h3>

  * [Configure server settings](/reference/settings/server-settings/settings)
  * [Set up security and access control](/concepts/features/security/access-rights)
  * [Configure hardware properly](/guides/oss/best-practices/tips)

  <br />

  <h3 id="database-management">
    Database management
  </h3>

  * [Create and manage databases](/reference/statements/create/database)
  * [Choose the right table engine](/reference/engines/table-engines)

  <br />

  <h3 id="data-operations">
    Data operations
  </h3>

  * [Optimize bulk data insertion](/concepts/features/operations/insert/bulkinserts)
  * [Handle data format problems](/reference/formats)
  * [Set up streaming data pipelines](/concepts/features/operations/insert/asyncinserts)
  * [Improve S3 integration performance](/integrations/connectors/data-ingestion/AWS/performance)

  <br />

  <h3 id="advanced-configuration">
    Advanced configuration
  </h3>

  * [Set up data replication](/reference/engines/table-engines/mergetree-family/replication)
  * [Configure distributed tables](/reference/engines/table-engines/special/distributed)

  - [Set up backup and recovery](/concepts/features/backup-restore/overview)
  - [Configure monitoring](/reference/system-tables/overview)
</Accordion>

<h2 id="still-need-help">
  Still need help?
</h2>

If you can't find a solution:

1. **Ask AI**
2. **Check system tables** - [Overview](/reference/system-tables/overview)
3. **Review server logs** - Look for error messages in your ClickHouse logs
4. **Ask the community** - [Join Our Community Slack](https://clickhouse.com/slack), [GitHub Discussions](https://github.com/ClickHouse/ClickHouse/discussions)
5. **Get professional support** - [ClickHouse Cloud support](https://clickhouse.com/support)