EXTENDED EPHEMERAL LOGGING - LOG STORAGE MANAGEMENT FOR APPLICATIONS WITH LONG-LIVED TRANSACTIONS

Extended ephemeral logging (XEL) is a new technique for managing a log of database activity subject to the general assumption that the lifet imes of an application's transactions may be statistically distributed over a wide range. The log resides on nonvolatile disk storage and pr ovides fault tolerance to system failures (in which the contents of vo latile main memory storage may be lost).XEL segments a log into a chai n of fixed-size FIFO queues and performs generational garbage collecti on on records in the log. Log records that are no longer necessary for recovery purposes are ''thrown away'' when they reach the head of a q ueue; only records that are still needed for recovery are forwarded fr om the head of one queue to the tail of the next. XEL does not require checkpoints, permits fast recovery after a crash and is well suited f or applications that have a wide distribution of transaction lifetimes . Quantitative evaluation of XEL via simulation indicates that it can significantly reduce the disk space required for the log, at the expen se of slightly higher bandwidth for log information and more main memo ry; the reduced size of the log permits much faster recovery after a c rash as well as cost savings. XEL can significantly reduce both the di sk space and the disk bandwidth required for log information in a syst em that has been augmented with a nonvolatile region of main memory.