The Design and Evaluation of a Magnetic/Optical Access Structure for Temporal Databases

Abstract

This paper describes a magnetic/optical access structure for append–only temporal databases. We formally define the properties of an access structure, called the MonotonicB+ -Tree (MBT), that is well suited for Write-Once Read Many optical disks. We present an insertion algorithm for the MBT that does not require splitting of index nodes and give the time analysis for this algorithm. We also describe a storage architecture where optical disks work in tandem with magnetic disks. Magnetic disks are used for storing current versions and recent past versions, whereas optical disks are dedicated for archiving older past versions. Our archiving techniques: (1) allow temporal data and the MBT access structure to span magnetic disks and optical disks; (2) minimize the overhead of the migration process by taking advantage of append–only nature of temporal databases; (3) gracefully handle object versions with very long time intervals so that the delay in the migration process is kept to minimum; and (4) ensure that no false magnetic or optical disk address lookup is performed during search operations by duplicating some closed versions on both magnetic and optical disks. To validate our claims for the efficiency of migration techniques, we analyze the performance of temporal access structures partitioned between magnetic and optical disks. We show that the migration process has a minimal effect on the search time. Our simulation identifies important parameters, and shows how they affect the performance of the temporal access structures. These include mean of version lifespan, block size, query time interval length, and total number of versions.