> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vortexiq.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Connections In Use, ClickHouse

> Connections In Use for ClickHouse instances. Tracked live in Vortex IQ Nerve Centre. How to read it, why it matters, and how to act on it.

**Card class:** [Non-Hero](/nerve-centre/overview#card-classes-explained)  •  **Category:** [Capacity](/nerve-centre/connectors#connectors-by-type)

## At a glance

> **Connections In Use** is the live count of open client connections on the ClickHouse server right now. It is the raw numerator behind [Connection Pool Saturation %](/nerve-centre/kpi-cards/clickhouse/connection-pool-saturation): how many of your allowed slots are occupied at this instant. For a DBA or SRE, it is the fastest read on "how busy is the front door?" A flat, low number is healthy; a number creeping toward `max_connections` is the early warning before clients start getting rejected.

|                    |                                                                                                                                                                                               |
| ------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **What it tracks** | Connections In Use for the selected period, read live from the server.                                                                                                                        |
| **Data source**    | The `TCPConnection` and `HTTPConnection` gauges in `system.metrics`, summed across native (port 9000) and HTTP (port 8123) interfaces.                                                        |
| **Time window**    | `RT` (real-time, refreshed on the live poll).                                                                                                                                                 |
| **Alert trigger**  | None on this card directly. The saturation gauge owns the threshold; pair with [Connection Pool Saturation %](/nerve-centre/kpi-cards/clickhouse/connection-pool-saturation) (alerts `>90%`). |
| **Roles**          | engineering, operations                                                                                                                                                                       |

## What it tracks

The card reports the absolute number of connections currently held against the ClickHouse server, not a percentage. ClickHouse exposes these as gauges in `system.metrics`: `TCPConnection` counts native protocol clients (drivers, `clickhouse-client`, internal distributed queries), and `HTTPConnection` counts REST and HTTP-interface clients (dashboards, the JDBC/ODBC bridge, ad-hoc `curl`). The card sums both so you see total front-door occupancy in one figure. Read it next to the `max_connections` server setting (default 1024, often lower on ClickHouse Cloud tiers) to judge headroom. A steady baseline with brief spikes during reporting peaks is normal; a baseline that climbs and never recedes usually means a client is leaking connections (a pool that opens but never closes).

## Reconciling against the source

Confirm the live count directly against the server with `SELECT metric, value FROM system.metrics WHERE metric IN ('TCPConnection','HTTPConnection')`, or inspect individual sessions with `SELECT * FROM system.processes`. On ClickHouse Cloud, the same metrics surface in the service Monitoring tab. Small differences from a hand-run query are expected: the figures are sampled at different instants, and Vortex IQ excludes its own polling connection from the headline.

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### Tracked live in Vortex IQ Nerve Centre

*Connections In Use* is one of hundreds of KPI pulses Vortex IQ tracks across ClickHouse and 70+ other ecommerce connectors. Nerve Centre runs the detection layer; Vortex Mind investigates the cause when something moves; Ask Viq lets you interrogate any number in plain English.

[Start for free](https://app.vortexiq.ai/login) or [book a demo](https://www.vortexiq.ai/contact-us) to see this metric running on your own data.