Design and Implementation of the Multiuser Index-based Data Access System

We have built a multiuser storage system named MIDAS (Multiuser Index-based Data Access System) which is intended to be used for a lower subsystem of database management systems running on UNIX. MIDAS implements a modified B+-tree structure for the sake of control of concurrent operations on a B+-tree index. To guarantee the more concurrent accesses to the system tables such as buffers, lock table, etc., MIDAS divides each system table into several independent partitions. A MIDAS database can have more than one disk volume and a file can be spread over several volumes to deal with very large files and databases. We overcame the flaws of the UNIX file system efficiently by implementing an extent-based disk manager by means of the raw device interface. We employed the two phase locking method in conjunction with multiple granularity to serialize executions of several transactions which access to shared databases. This paper addresses the design rationales incorporated within the implementation, system architecture and results of the benchmark which was carried out in order to verify the design and implementation decisions.