---
title: "ClickHouse"
description: "Connect ClickHouse so OpenSRE can inspect query activity and system health during investigations"
---

OpenSRE queries ClickHouse system tables to surface slow queries, active connections, replica status, and table statistics — helping diagnose database performance issues during alert investigations.

## Prerequisites

- ClickHouse 21.x or later
- Network access from the OpenSRE environment to your ClickHouse instance
- A user with read access to system tables

## Setup

### Option 1: Interactive CLI

```bash
opensre integrations setup
```

Select **ClickHouse** when prompted and provide your host and credentials.

### Option 2: Environment variables

Add to your `.env`:

```bash
CLICKHOUSE_HOST=your-clickhouse-host
CLICKHOUSE_PORT=8123
CLICKHOUSE_DATABASE=default
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=your-password
CLICKHOUSE_SECURE=false   # set to true for HTTPS
```

| Variable | Default | Description |
| --- | --- | --- |
| `CLICKHOUSE_HOST` | — | **Required.** ClickHouse hostname or IP |
| `CLICKHOUSE_PORT` | `8123` | HTTP(S) port (8123 for HTTP, 8443 for HTTPS) |
| `CLICKHOUSE_DATABASE` | `default` | Default database |
| `CLICKHOUSE_USER` | `default` | Username |
| `CLICKHOUSE_PASSWORD` | — | Password |
| `CLICKHOUSE_SECURE` | `false` | Use HTTPS (`true`/`false`) |

### Option 3: Persistent store

```json
{
  "version": 1,
  "integrations": [
    {
      "id": "clickhouse-prod",
      "service": "clickhouse",
      "status": "active",
      "credentials": {
        "host": "your-clickhouse-host",
        "port": 8443,
        "database": "default",
        "username": "opensre_readonly",
        "password": "your-password",
        "secure": true
      }
    }
  ]
}
```

## Creating a read-only user

```sql
CREATE USER opensre_readonly IDENTIFIED BY 'secure-password';
GRANT SELECT ON system.* TO opensre_readonly;
GRANT SELECT ON default.* TO opensre_readonly;
```

## Investigation tools

When OpenSRE investigates a ClickHouse-related alert, three diagnostic tools are available:

- **Query activity** — reads `system.query_log` to surface recent slow and failed queries
- **System health** — reads `system.metrics` for active connections, query count, replica status, and uptime
- **Table stats** — reads `system.parts` for table-level row counts and storage sizes

All operations are read-only.

## Verify

```bash
opensre integrations verify clickhouse
```

Expected output:

```
Service: clickhouse
Status: passed
Detail: Connected to ClickHouse 23.8.1; database: default
```

## Troubleshooting

| Symptom | Fix |
| --- | --- |
| **Connection refused** | Check host, port, and firewall. Use port `8443` with `CLICKHOUSE_SECURE=true` |
| **Authentication failed** | Verify username and password |
| **SSL error** | Set `CLICKHOUSE_SECURE=true` and use port `8443` |
| **Access denied on system tables** | Grant `SELECT ON system.*` to the OpenSRE user |

## Security best practices

- Create a **dedicated read-only user** with access only to `system.*` and the databases OpenSRE needs.
- Use **HTTPS** (`CLICKHOUSE_SECURE=true`) in production.
- Store credentials in `.env`, not in source code.