| ## Control connection |
| |
| The control connection is a dedicated connection used for administrative tasks: |
| |
| * querying system tables to learn about the cluster's [topology](../metadata/node/) and |
| [schema](../metadata/schema/); |
| * checking [schema agreement](../metadata/schema/#schema-agreement); |
| * reacting to server events, which are used to notify the driver of external topology or schema |
| changes. |
| |
| When the driver starts, the control connection is established to the first contacted node. If that |
| node goes down, a [reconnection](../reconnection/) is started to find another node; it is governed |
| by the same policy as regular connections (`advanced.reconnection-policy` options in the |
| [configuration](../configuration/)), and tries the nodes according to a query plan from the |
| [load balancing policy](../load_balancing/). |
| |
| The control connection is managed independently from [regular pooled connections](../pooling/), and |
| used exclusively for administrative requests. It shows up in [Node.getOpenConnections], as well as |
| the `pool.open-connections` [metric](../metrics); for example, if you've configured a pool size of |
| 2, the control node will show 3 connections. |
| |
| There are a few options to fine tune the control connection behavior in the |
| `advanced.control-connection` and `advanced.metadata` sections; see the [metadata](../metadata/) |
| pages and the [reference configuration](../configuration/reference/) for all the details. |
| |
| [Node.getOpenConnections]: https://docs.datastax.com/en/drivers/java/4.7/com/datastax/oss/driver/api/core/metadata/Node.html#getOpenConnections-- |
