Introduction

The DB2 for Linux, UNIX, and Windows High Availability Disaster Recovery (HADR) feature is a database replication feature that provides a high availability solution for both partial and complete site failures. HADR protects against data loss by replicating data changes from a source database called the primary, to a target database called the standby.

HADR was introduced in DB2 V8.2. Before DB2 V9.7 Fix Pack 1, the standby server only rolled forward the log records shipped from the primary server and was offline to users. No user connections were allowed on the standby database.

Starting with DB2 V9.7 Fix Pack 1, the reads on standby feature (HADR RoS) enables read-only applications to access the standby database. This is possible only when the reads on standby feature is enabled. With this feature read/write applications can access the HADR primary database, and read-only applications can access the primary or the standby databases. This enables you to offload some of the read-only workload running on the primary to the standby. Applications connecting to the standby database do not affect the availability of the standby in case of a failover.

This article explains how to set up the reads on standby feature for reading on standby, and discusses the limitations of reading from the current standby. In addition, it includes suggestions for utilizing the potential of the standby database. The article assumes the reader is familiar with setting up a HADR pair.

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