Improving Data Consistency in Mobile Computing Using Isolation

Improving Data Consistency in Mobile Computing Using Isolation

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Improving Data Consistency in Mobile Computing Using Isolation-Only Transactions Qi Lu M. Satyanarayanan School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213 luqi,satya @cs.cmu.edu Abstract Disconnected operation is an important technique for providing mobile access to shared data in distributed file systems. However, data inconsistency resulting from par- titioned sharing remains a serious concern. This paper presents a new mechanism called isolation-only transac- tion(IOT) that uses serializability constraints to automat- ically detect read/write conflicts. The IOT consistency model provides a set of options for automatic and manual conflict resolution. In addition, application specific knowl- edge can be incorporated to detect and resolve conflicts. To preserve upward Unix compatibility, the IOT mecha- nism is provided as an optional file system facility and its flexible interfaces allow any existing Unix application to be executed as an IOT. This paper describes high level sys- tem design and implementationand concludes with related work and current status. 1 Introduction Disconnected operation based on an optimistic replica control strategy has proved to be a viable technique for mobile file access[9]. There is now considerable evidence that write/write conflicts, which dominated early discus- sions of optimistic replication, are relatively rare and can often be transparently resolved[10, 11, 12, 18]. But actual experience indicates that read/write conflicts, traditionally ignored in file systems, deserve much greater attention in disconnected operation. The possibility of read/write conflicts exists even in timesharing file systems: for example, consider the in- stallation of a new version of a library by one user while another user is building executables that link in the library. Although such conflicts are rare in timesharing or worksta- tion environments, the analogous scenario in mobile com- puting is far more likely to lead to read/write conflicts. Two factors account for this. First, long periods of discon- nection significantly enlarge the window of vulnerability. This research was supported by the Air Force Materiel Command (AFMC) and ARPA under contract number F196828-93-C-0193. Addi- tional support was provided by the IBM Corporation, Digital Equipment Corporation, and Intel Corporation. Second, explicituser coordinationtoavoid conflictsis more difficult. Consider the following example of a partitioned read/write conflict. A programmer Joe caches relevant files on his laptop for a weekend trip. While disconnected, he edits some source files and builds a new version of cfs , a file system utility program. But one of the libraries libutil.a that is linked in is updated on the servers during Joes absence. Here the linking and updating of libutil.a constitute a read/write conflict, leaving cfs in a possible unsatisfactory state. The consequences of un- detected read/write conflicts can be especially painful if the...
View Full Document

Page1 / 5

Improving Data Consistency in Mobile Computing Using Isolation

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online