Research On Embedded Database Recovery Algorithm

With the development of embedded technology, embedded database has been used more and more widely. Embedded environment has many characteristics and limitations, such as mobility, network instability and power supply ability, reliability and performance of the embedded database has put forward higher requirements and challenges, a strong recovery subsystem is an important part of the embedded database’s component. Through the systematic research on the database recovery technology, we study and improve the recovery subsystem in embedded Database Management System, to improve the system reliability and availability.In order to adapt to the embedded environment, system design follows the simple rules. The rollback segment is designed and improved, it is integrated into the data file. When system restoring, only searches the reserved rollback segment, it saves the recovery time; at the same time the log file is designed into a single log file form, using transaction consistency checkpoint to shorten the recovery process when needs to scan the log volume during system startup.When system needs restore, we design and put the selective-redo into implementation to avoid to redo all the Redo logs. For those records which have written to the database file, according to page LSN(Log Sequence Number) and log LSN’s judgment, decides whether to redo the log record, rather than blindly. Then, we analyze the premise condition when using the selective-redo method. The method saves system buffer, reduces the I/O overloads and embodies the micro kernel requirements of embedded database.In order to make full use of the operating system’s multiprogramming design thought and the special transaction model that the system uses, system restore uses multiple threads to redo log records. The use of a log distribution thread multiple redo thread model, synchronization between thread to complete cooperation historical operation, achieves rapid reconstruction of the system state when system crashes.Tests show that, the improved recovery subsystem not only can handle transaction failure, system failure and media failure, which may occurs during system processing, but also can shorten the time of recovery.