– 1 – A Log – Structured History Data Access Method ( LHAM ) September 4 , 1993

There are numerous applications that require on–line access to a history of business events. Ideally, both historical and current data should be logically integrated into some form of temporal database, also known as a multi– version database, historical database, or rollback database. The underlying access method should support the migration of old record versions onto inexpensive write–once media, different forms of “time–travel” queries, and potentially high rates of update events. This paper introduces a new access method for history data, called the Log–structured History data Access Method (LHAM). The basic principle of LHAM is to partition the data into successive components based on the timestamps of the record versions, and to employ a rolling merge process for efficient data migration between components. The concept of a rolling merge process was introduced in [OCGO92] with the Log–Structured Merge Tree (LSM–tree).