Active standby nodes

An active standby node exists is a node in an Enterprise Mode database that is available to replace any failed node.

1: Creating an active standby node
2: Replace a node with an active standby node
3: Revert active standby nodes

An active standby node exists is a node in an Enterprise Mode database that is available to replace any failed node. Unlike permanent Vertica nodes, an standby node does not perform computations or contain data. If a permanent node fails, an active standby node can replace the failed node, after the failed node exceeds the failover time limit. After replacing the failed node, the active standby node contains the projections and performs all calculations of the node it replaced.

In this section

1 - Creating an active standby node

You can create active standby nodes in an Enterprise Mode database at the same time that you create the database, or later.

Note

When you create an active standby node, be sure to add any necessary storage locations. For more information, refer to Adding Storage Locations.

Creating an active standby node in a new database

Create a database, including the nodes that you intend to use as active standby nodes.
Using vsql, connect to a node other than the node that you want to use as an active standby node.
Use ALTER NODE to convert the node from a permanent node to an active standby node. For example:
```
=> ALTER NODE v_mart_node5 STANDBY;
```
After you issue the ALTER NODE statement, the affected node goes down and restarts as an active standby node.

Creating an active standby node in an existing database

When you create a node to be used as an active standby node, change the new node to ephemeral status as quickly as possible to prevent the cluster from moving data to it.

Add a node to the database.

Important
Do not rebalance the database at this stage.
Using vsql, connect to any other node.
Use ALTER NODE to convert the new node from a permanent node to an ephemeral node. For example:
```
=> ALTER NODE v_mart_node5 EPHEMERAL;
```
Rebalance the cluster to remove all data from the ephemeral node.
Use ALTER NODE on the ephemeral node to convert it to an active standby node. For example:
```
=> ALTER NODE v_mart_node5 STANDBY;
```

2 - Replace a node with an active standby node

A failed node on an Enterprise Mode database can be replaced with an active standby node automatically, or manually.

Important

A node must be down before it can be replaced with an active standby node. Attempts to replace a node that is up return with an error.

Automatic replacement

You can configure automatic replacement of failed nodes with parameter FailoverToStandbyAfter. If enabled, this parameter specifies the length of time that an active standby node waits before taking the place of a failed node. If possible, Vertica selects a standby node from the same fault group as the failed node. Otherwise, Vertica randomly selects an available active standby node.

Manual replacement

As an administrator, you can manually replace a failed node with ALTER NODE:

Connect to the database with Administration Tools or vsql.
Replace the node with ALTER NODE...REPLACE. The REPLACE option can specify a standby node. If REPLACE is unqualified, then Vertica selects a standby node from the same fault group as the failed node, if one is available; otherwise, it randomly selects an available active standby node.

3 - Revert active standby nodes

When a down node in an Enterprise Mode database is ready for reactivation, you can restore it by reverting its replacement to standby status.

When a down node in an Enterprise Mode database is ready for reactivation, you can restore it by reverting its replacement to standby status. You can perform this operation on individual nodes or the entire database, with ALTER NODE and ALTER DATABASE, respectively:

Connect to the database with Administration Tools or via vsql.
Revert the standby nodes.
- Individually with ALTER NODE:
```
ALTER NODE node-name RESET;
```
- Collectively across the database cluster with ALTER DATABASE:
```
ALTER DATABASE DEFAULT RESET STANDBY;
```

If a down node cannot resume operation, Vertica ignores the reset request and leaves the standby node in place.