Glossary

This glossary describes terms used in this book. For a description of Adaptive Server and SQL terms, refer to the Adaptive Server Glossary.

Asymmetrical

A high availability system consisting of one primary companion and one secondary companion. In an asymmetric system, only the primary companion can failover. In this system, the secondary Adaptive Server is also known as a “hot stand-by.”

Companion Server

Each Adaptive Server in a high availability system is a companion. One of the Adaptive Servers is a companion (see below for definition) and the other is the secondary companion (see below for definition).

Cluster

A collection of nodes in a high availability system. A cluster for the Adaptive Server high availability system consists of two nodes.

Failback

The planned event during which Adaptive Server is migrated back to, and restarted on, the original machine. This involves moving the failed-over databases, devices, and client connections from the secondary companion to the restarted primary companion.

Failover

During failover, Adaptive Server migrates to another machine which takes over the responsibility of managing the failed over Adaptive Server. Failover can occur because of either a scheduled maintenance or a failure of Adaptive Server or the machine running Adaptive Server.

Failover Mode

The mode of the primary companion after it has failed over and is running on the secondary companion.

High Availability

A system that is designed to reduce the amount of downtime a system suffers.

Node

A machine in a high availability system.

Normal Companion Mode

The mode during which two Adaptive Servers in a high availability system are functioning as independent servers and are configured to failover during a scheduled maintenance or system failure.

Primary companion

The Adaptive Server whose databases and connections are migrated to the secondary Adaptive Server during failover.

Proxy Databases

Place holder databases created on the secondary companion for every user database on the primary companion. Proxy databases reserve the database names so that during failover, all database names are unique on the system. For more information about proxy databases, see Chapter 5, “Proxy Databases, User Databases, and Proxy System Tables”

Secondary companion

The Adaptive Server configured to accept the failed over primary Adaptive Server during failover

Single-Server Mode

The mode of Adaptive Server when it is being configured for high availability. During this mode, Adaptive Server cannot failover.

Suspended Companion Mode

The mode of Adaptive Server after companion mode has been suspended. During this mode, Adaptive Server cannot failover; it is working independently of the other Adaptive Server.

Symmetrical

A high availability system in which two independent Adaptive Servers act as failover servers for each other. That is, each Adaptive Server acts as both a primary and a secondary companion.