## Preflight checks for ClickHouse

URL: https://docs.atlan.com/apps/connectors/database/clickhouse/references/preflight-checks-for-clickhouse

> Before running the ClickHouse crawler, you can run preflight checks to perform the necessary technical validations.

Before [running the ClickHouse crawler](https://docs.atlan.com/llms/connectors/clickhouse/crawl-clickhouse/llms.txt), you can run [preflight checks](https://docs.atlan.com/llms/catalog/connector-capabilities/what-are-preflight-checks/llms.txt) to perform the necessary technical validations. The following preflight checks are completed:

## Connection test

✅ `Connection test passed`

❌ `Connection test failed: <error message>`

Validates that Atlan can establish a connection to your ClickHouse instance using the provided host, port, and credentials.

## System tables access

✅ `System tables access check passed`

❌ `System tables access check failed: <error message>`

Validates that the configured user has SELECT access to `system.tables`, which is required for extracting table and view metadata.

## Database access

✅ `Database access check passed`

❌ `Database access check failed: <error message>`

Validates that the configured user has SELECT access to `system.databases`, which is required for discovering available databases.

## Column metadata access

✅ `Column metadata access check passed`

❌ `Column metadata access check failed: <error message>`

Validates that the configured user has SELECT access to `system.columns`, which is required for extracting column-level metadata.

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