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    • 97. 发明授权
    • System and method for a snapshot query during database recovery
    • 数据库恢复期间快照查询的系统和方法
    • US07146386B2
    • 2006-12-05
    • US10812188
    • 2004-03-29
    • Wei Xiao
    • Wei Xiao
    • G06F17/30
    • G06F17/30533G06F11/1471G06F11/2074G06F17/30362G06F17/30371Y10S707/99938Y10S707/99944Y10S707/99953
    • A method of performing a snapshot query in a database undergoing recovery allows access to the database during rollback or undo operations. The method includes allowing the query to detect whether a redo lock is present on a data item and if so, waiting until subsequent rollback operations release the lock. If another user has placed an exclusive lock on a data item of the database, the query may continue by reading a version of the data item form the version store. In an embodiment where a mirror database is used for recovery, the constant redo operations have an associated version store. Upon failover to the mirror database, queries may begin during the undo phase of recovery by allowing a query to read the version store of redo operations.
    • 在正在进行恢复的数据库中执行快照查询的方法允许在回滚或撤消操作期间访问数据库。 该方法包括允许查询检测数据项上是否存在重做锁,如果是,则等待直到后续回滚操作释放锁。 如果另一用户已经对数据库的数据项放置了排他锁,则可以通过从版本存储器读取数据项的版本来继续查询。 在使用镜像数据库进行恢复的实施例中,常数重做操作具有关联的版本存储。 在故障切换到镜像数据库时,可以在恢复的撤消阶段期间开始查询,方法是允许查询读取重做操作的版本存储。