Research On Recovery Mechanisms In DM Embedded DBMS

With the development of embedded technology, embedded database has been used moreand more widely. Embedded environment has many characteristics and limitations, suchas mobility, network instability and power supply ability, reliability and performance ofthe embedded database has put forward higher requirements and challenges, a strongrecovery subsystem is an important part of the embedded database’s component. Throughthe systematic research on the database recovery technology, we study and improve therecovery subsystem in DM embedded Database Management System, to improve thesystem 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. Whensystem 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 transactionconsistency checkpoint to shorten the recovery process when needs to scan the log volumeduring system startup.When system needs restore, we design and put the selective-redo into implementation toavoid 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 whetherto redo the log record, rather than blindly. Then, we analyze the premise condition whenusing the selective-redo method. The method saves system buffer, reduces the I/Ooverloads and embodies the micro kernel requirements of embedded database.In order to make full use of the operating system’s multiprogramming design thoughtand the special transaction model that the system uses, system restore uses multiplethreads to redo log records. The use of a log distribution thread multiple redo thread model,synchronization between thread to complete cooperation historical operation, achievesrapid 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, butalso can shorten the time of recovery.