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

## Performance and errors[​](#performance-and-errors "Direct link to 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[​](#query-performance "Direct link to Query performance")

- [Find which queries are using the most resources](/docs/knowledgebase/find-expensive-queries)
- [Complete query optimization guide](/docs/optimize/query-optimization)
- [Optimize JOIN operations](/docs/best-practices/minimize-optimize-joins)
- [Run diagnostic queries to find bottlenecks](/docs/knowledgebase/useful-queries-for-troubleshooting)

  

### Data insertion performance[​](#data-insertion-performance "Direct link to Data insertion performance")

- [Speed up data insertion](/docs/optimize/bulk-inserts)
- [Set up asynchronous inserts](/docs/optimize/asynchronous-inserts)

  

### Advanced analysis tools[​](#advanced-analysis-tools "Direct link to Advanced analysis tools")

- [Check what processes are running](/docs/knowledgebase/which-processes-are-currently-running)
- [Monitor system performance](/docs/operations/system-tables/processes)

  

### Error messages[​](#error-messages "Direct link to Error messages")

- **"Memory limit exceeded"** → [Debug memory limit errors](/docs/guides/developer/debugging-memory-issues)
- **"Connection refused"** → [Fix connection problems](#connections-and-authentication)
- **"Login failures"** → [Set up users, roles, and permissions](/docs/operations/access-rights)
- **"SSL certificate errors"** → [Fix certificate problems](/docs/knowledgebase/certificate_verify_failed_error)
- **"Table/database errors"** → [Database creation guide](/docs/sql-reference/statements/create/database) | [Table UUID problems](/docs/engines/database-engines/atomic)
- **"Network timeouts"** → [Network troubleshooting](/docs/interfaces/http)
- **Other issues** → [Track errors across your cluster](/docs/operations/system-tables/errors)

## Memory and resources[​](#memory-and-resources "Direct link to Memory and resources")

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

**Show memory solutions**

### Memory debugging and monitoring:[​](#memory-debugging-and-monitoring "Direct link to Memory debugging and monitoring:")

- [Identify what's using memory](/docs/guides/developer/debugging-memory-issues)
- [Check current memory usage](/docs/operations/system-tables/processes)
- [Memory allocation profiling](/docs/operations/allocation-profiling)
- [Analyze memory usage patterns](/docs/operations/system-tables/query_log)

  

### Memory configuration:[​](#memory-configuration "Direct link to Memory configuration:")

- [Configure memory limits](/docs/operations/settings/memory-overcommit)
- [Server memory settings](/docs/operations/server-configuration-parameters/settings)
- [Session memory settings](/docs/operations/settings/settings)

  

### Scaling and sizing:[​](#scaling-and-sizing "Direct link to Scaling and sizing:")

- [Right-size your service](/docs/operations/tips)
- [Configure automatic scaling](/docs/manage/scaling)

## Connections and Authentication[​](#connections-and-authentication "Direct link to Connections and Authentication")

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

**Show connection solutions**

### Basic Connection issues[​](#basic-connection-issues "Direct link to Basic Connection issues")

- [Fix HTTP interface issues](/docs/interfaces/http)
- [Handle SSL certificate problems](/docs/knowledgebase/certificate_verify_failed_error)
- [User authentication setup](/docs/operations/access-rights)

  

### Client interfaces[​](#client-interfaces "Direct link to Client interfaces")

- [Native ClickHouse clients](/docs/interfaces/natives-clients-and-interfaces)
- [MySQL interface problems](/docs/interfaces/mysql)
- [PostgreSQL interface issues](/docs/interfaces/postgresql)
- [gRPC interface configuration](/docs/interfaces/grpc)
- [SSH interface setup](/docs/interfaces/ssh)

  

### Network and data[​](#network-and-data "Direct link to Network and data")

- [Network security settings](/docs/operations/server-configuration-parameters/settings)
- [Data format parsing issues](/docs/interfaces/formats)

## Setup and configuration[​](#setup-and-configuration "Direct link to Setup and configuration")

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

**Show setup and configuration solutions**

### Initial setup[​](#initial-setup "Direct link to Initial setup")

- [Configure server settings](/docs/operations/server-configuration-parameters/settings)
- [Set up security and access control](/docs/operations/access-rights)
- [Configure hardware properly](/docs/operations/tips)

  

### Database management[​](#database-management "Direct link to Database management")

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

  

### Data operations[​](#data-operations "Direct link to Data operations")

- [Optimize bulk data insertion](/docs/optimize/bulk-inserts)
- [Handle data format problems](/docs/interfaces/formats)
- [Set up streaming data pipelines](/docs/optimize/asynchronous-inserts)
- [Improve S3 integration performance](/docs/integrations/s3/performance)

  

### Advanced configuration[​](#advanced-configuration "Direct link to Advanced configuration")

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

- [Set up backup and recovery](/docs/operations/backup/overview)
- [Configure monitoring](/docs/operations/system-tables/overview)

## Still need help?[​](#still-need-help "Direct link to Still need help?")

If you can't find a solution:

1. **Ask AI** - [Ask AI](#) for instant answers.
2. **Check system tables** - [Overview](/docs/operations/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)

- [Performance and errors](#performance-and-errors)
  - [Query performance](#query-performance)- [Data insertion performance](#data-insertion-performance)- [Advanced analysis tools](#advanced-analysis-tools)- [Error messages](#error-messages)- [Memory and resources](#memory-and-resources)
    - [Memory debugging and monitoring:](#memory-debugging-and-monitoring)- [Memory configuration:](#memory-configuration)- [Scaling and sizing:](#scaling-and-sizing)- [Connections and Authentication](#connections-and-authentication)
      - [Basic Connection issues](#basic-connection-issues)- [Client interfaces](#client-interfaces)- [Network and data](#network-and-data)- [Setup and configuration](#setup-and-configuration)
        - [Initial setup](#initial-setup)- [Database management](#database-management)- [Data operations](#data-operations)- [Advanced configuration](#advanced-configuration)- [Still need help?](#still-need-help)

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