Improved availability of data

Db2 data sharing helps you meet your service objective by improving availability during both planned and unplanned outages.

As the following figure illustrates, if one subsystem fails, users can access their Db2 data from another subsystem. Transaction managers are informed that Db2 is down and can switch new user work to another Db2 subsystem in the group. For unplanned outages, the z/OS automatic restart manager can automate restart and recovery.

Begin figure description. If a subsystem fails in a two-member data sharing group, new application requests are automatically directed to the functioning member. End figure description. — Figure 1. How data sharing improves availability during outages. If a Db2 subsystem or the entire central processor complex (CPC) fails, work can be routed to another system.

Although the increased availability of Db2 has some performance cost, the overhead for interprocessor communication and caching changed data is minimized. Db2 provides efficient locking and caching mechanisms and uses coupling facility hardware. A coupling facility is a special logical partition that runs the coupling facility control program. It provides high-speed caching, list processing, and locking functions in a Sysplex. The Db2 structures in the coupling facility benefit from high availability. The coupling facility uses automatic structure rebuild and duplexing of the structures that are used for caching data.