Continuously available database server having multiple groups of nodes with minimum intersecting sets of database fragment replicas

US5555404A · kind A · utility

Assignee

• Telenor ASA · NO

Inventors

• .O slashed.ystein Torbj.o slashed.rnsen · Trondheim, NO
• Svein-Olaf Hvasshovd · Trondheim, NO

Key dates

• Filing date: May 26, 1995
• Grant date: Sep 10, 1996
• Expiry date: May 26, 2015

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10S707/99953
• WIPO field: Computer technology
• WIPO sector: Electrical engineering

Abstract

A database server with a "shared nothing" system architecture has multiple nodes, each having its own central processing unit, primary and secondary memory for storing database tables and other data structures, and communication channels for communication with other ones of the nodes. The nodes are divided into at least two groups that share no resources. Each database table in the system is divided into fragments distributed for storage purposes over all the nodes in the system. To ensure continued data availability after a node failure, a "primary replica" and a "standby replica" of each fragment are each stored on nodes in different ones of the groups. Database transactions are performed using the primary fragment replicas, and the standby replicas are updated using transaction log records. Every node of the system includes a data dictionary that stores information indicating where each primary and standby fragment replica is stored. The fragments are allocated as evenly as possible among the system nodes using a fragment to node assignment equation. A transaction manager on each node responds to database queries by determining which fragment of a database is being accessed by t…