Shadow Logging - An Efficient Transaction Recovery Method

In this paper, we present LU-Logging, an efficient transaction recovery method. The method is based on (flexible-redo/minimal-undo) algorithm. The paper describes an implementation which avoids the overheads of deferred updating used in previous no-undo implementations. An update by a transaction to a data record does not immediately update the data record. Instead, it generates a redo log record and associates it with the data page. Each page in the data base has an associated log page, which contains the still-uncommitted log records of the updates for the data page. The log page is read from and written to the disk along with the corresponding data page. This gives the flexibility of applying the redo log records any time after the transaction commits, in particular when the data page is read by another transaction. We call this updating as lazy. For aborted transactions the redo log records are just discarded. Simulation studies show that the overhead during normal transaction processing for LU-Logging is comparable to that of traditional logging. The crash recovery time is shown to be an order of magnitude faster than that for traditional logging