the Communications Web site, http://cacm.acm.org,
features more than a dozen bloggers in the BLoG@cacm
community. in each issue of Communications, we’ll publish
selected posts or excerpts.
follow us on twitter at http://twitter.com/blogcacm
DOI: 10.1145/1831407.1831411
http://cacm.acm.org/blogs/blog-cacm
in Search of
Database consistency
Michael Stonebraker discusses the implications of
the CAP theorem on database management system applications
that span multiple processing sites.

michael Stonebraker “errors in Database Systems, eventual consistency, and the caP theorem” http://cacm.acm.org/ blogs/blog-cacm/83396 Recently, there has been considerable renewed interest in the CAP theorem1 for database management system (DBMS) applications that span multiple processing sites. In brief, this theorem states that there are three interesting properties that could be desired by DBMS applications:

C: Consistency. The goal is to allow multisite transactions to have the familiar all-or-nothing semantics, commonly supported by commercial DBMSs. In addition, when replicas are supported, one would want the replicas to always have consistent states.

A: Availability. The goal is to support a DBMS that is always up. In other words, when a failure occurs, the system should keep going, switching over to a replica, if required. This feature was popularized by Tandem Computers more than 20 years ago.

P: Partition-tolerance. If there is a
network failure that splits the process-
ing nodes into two groups that cannot
talk to each other, then the goal would
be to allow processing to continue in
both subgroups.