A fundamental element in the design of a highly available system is the ability to recover quickly from a failure. Failures may be related to hardware problems such as system failures or network failures. Software failures include operating system failure, application failure, database failure and operator error.
Your replicated system must employ a cluster manager or custom software to detect such failures and, in the event of a failure involving a master database, redirect the user load to one of its subscribers. The focus of this discussion is on the TimesTen mechanisms that an application or cluster manager can use to recover from failures.
Unless the replication scheme is configured to use the return twosafe service, TimesTen replicates updates only after the original transaction commits to the master database. If a subscriber database is inoperable or communication to a subscriber database fails, updates at the master are not impeded. During outages at subscriber systems, updates intended for the subscriber are saved in the TimesTen transaction log.
The procedures described in this chapter require the