Philip B Bernstein

US Patent:

52127885, May 18, 1993

Filed:

May 22, 1990

Appl. No.:

7/527087

Inventors:

David B. Lomet - Westford MA
Philip A. Bernstein - Carlisle MA
James Johnson - Newbury, GB2
Kenneth Wilner - Merrimack NH

Assignee:

Digital Equipment Corporation - Maynard MA

International Classification:

G06F 700
G06F 1540

US Classification:

395600

Abstract:

A distributed database system has a plurality of databases located at distinct nodes, at least one of the databases comprising a timestamping database. Distributed transactions are committed using a two phase protocol. During the first phase, each cohort to the transaction votes to commit or abort the transaction, and also votes an earliest time and a latest time at which the transaction is to be committed. If all the cohorts vote to commit the transaction and the intersection of the voted time ranges is not empty, then the transaction is committed during the second phase of the protocol. A transaction time is selected from the intersection of the voted time ranges and is used to timestamp all updated data that is durably stored when the transaction is committed. Before the first phase of the two phase commit protocol, each transaction read or write locks data at each node for which it needs read or write access. Whenever a transaction enters the first phase of the commit protocol, read locks for that transaction can be converted into delay locks.