# Overview

> The landing page for each ClickHouse host: instant health status, active queries, memory, disk, and CPU at a glance.

| | |
|---|---|
| **Routes** | `/overview` |
| **Feature id** | `overview` |
| **Default access** | `public` |
| **Requires auth** | No (set `CHM_FEATURE_OVERVIEW_ACCESS=authenticated` to gate) |
| **System tables** | `system.asynchronous_metrics`, `system.metrics`, `system.processes`, `system.disks`, `system.tables` |
| **ClickHouse grants** | `SELECT` on the system tables above |

## What it does

Overview is the first page you land on. It pulls live numbers from several system tables to answer:

- Is the server healthy right now?
- How many queries are running?
- How much memory and disk are in use?
- What is CPU load?

The page is organized into tabs: **Connections**, **Queries**, **Merges**, **Replication**, and **System**. Each tab shows a small set of charts that auto-refresh. There are no write operations on this page.

## Pages

| Page | Route | What it shows | System tables |
|---|---|---|---|
| Overview | `/overview` | CPU, memory, disk gauges; active query count; connection count; replication lag indicator | `system.asynchronous_metrics`, `system.metrics`, `system.processes`, `system.disks`, `system.tables` |

## Permissions & access

Overview is public by default. To restrict it:

```bash
## Env var
CHM_FEATURE_OVERVIEW_ACCESS=authenticated
```

```toml
## CHM_CONFIG_FILE (TOML)
[features.overview]
access = "authenticated"
```

To disable the feature entirely:

```bash
CHM_DISABLED_FEATURES=overview
## or
CHM_FEATURE_OVERVIEW_ENABLED=false
```

When disabled, the route is removed from the nav and a disabled screen is shown on direct visit.

## Configuration

No feature-specific configuration. The refresh interval and caching behaviour follow the global settings:

```bash
CLICKHOUSE_MAX_EXECUTION_TIME=60   # query timeout in seconds
```

## Notes & limitations

- `system.asynchronous_metrics` values are recalculated by ClickHouse on a background interval (default ~1 s). The values shown are as fresh as that interval allows.
- `system.disks` reports the disks ClickHouse knows about. If you use multiple storage policies or remote disks (S3, HDFS), all configured disks appear.
- `system.tables` is queried to derive a table count. On clusters with many databases this can be slow; increase `CLICKHOUSE_MAX_EXECUTION_TIME` if overviews time out.
- The Replication tab shows replication lag only when replicated tables exist on the host. The tab still appears even if there are none.

## Related

- [Authentication](/authentication)
- [Settings reference](/settings)
- [Health alerting](/features/health)