When a planned or unplanned outage is complete, a DBA can initiate a full system recovery to bring the system back to the active state by re-running all the requests sent in managed sessions. The time to recover depends on such factors as the size of the Teradata system and the concurrency of the workloads. In a typical environment that includes a mixture of applications performing reads and writes, the recovery of a system takes less than the total time the system was down. During the recovery, system only needs to re-run the write requests that were missed.
In a workload with numerous write requests, with little or no read traffic, the time to recover a system may be longer and may equal the time of the outage. For example, it happens if the client workload continues to drive the active systems at their full throughput while the recovery system is trying to catch up. While the system is recovering, Unity recovery log and data file system provide the recovering system extra capacity to sync. The log and data files store incoming write requests at the top of the recovery queue as the recovering system is re-running them from the bottom of the queue.