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Resolving File Conflicts in the Ficus File System

Peter Reiher, John S. Heidemann, David Ratner, Gregory Skinner, and Gerald J. Popek
USC/Information Sciences Institute

Abstract

Ficus is a flexible replication facility with optimistic concurrency control designed to span a wide range of scales and network environments. Optimistic concurrency control provides rapid local access and high availability of files for update in the face of disconnection, at the cost of occasional conflicts that are only discovered when the system is reconnected. Ficus reliably detects all possible conflicts. Many conflicts can be automatically resolved by recognizing the file type and understanding the file's semantics. This paper describes experiences with conflicts and automatic conflict resolution in Ficus. It presents data on the frequency and character of conflicts in our environment. This paper also describes how semantically knowledgeable resolvers are designed and implemented, and discusses our experiences with their strengths and limitations. We conclude from our experience that optimistic concurrency works well in at least one realistic environment, conflicts are rare, and a large proportion of those conflicts that do occur can be automatically solved without human intervention.

Availability

This paper is available in several formats: abstract web page with pointers and cites, gzip'ed postscript, PDF, paper copies can be obtained by mail to the authors. Copyright terms for this paper appear below.

Reference

Reiher94a: Peter Reiher, John S. Heidemann, David Ratner, Gregory Skinner, and Gerald J. Popek. Resolving File Conflicts in the Ficus File System. In USENIX Conference Proceedings, pp. 183-195. Boston, MA, USENIX. June, 1994. <http://www.isi.edu/~johnh/PAPERS/Reiher94a.html>.

@inproceedings{Reiher94a,
	author = "Peter Reiher and John S. Heidemann and David Ratner and Gregory Skinner and Gerald J. Popek",
	title = "Resolving File Conflicts in the {Ficus} File System",
	booktitle = " {USENIX} Conference Proceedings",
	year = "1994",
	month = "June",
	address = "Boston, MA",
	publisher = "{USENIX}",
	pages = "183--195",
	keywords = "ficus, conflict resolution",
	url = "http://www.isi.edu/~johnh/PAPERS/Reiher94a.html",
	psurl = "http://www.isi.edu/~johnh/PAPERS/Reiher94a.ps.gz",
	pdfurl = "http://www.isi.edu/~johnh/PAPERS/Reiher94a.pdf",
	oldurl = "ftp://ftp.cs.ucla.edu/pub/ficus/usenix_summer_94_resolver.ps.gz",
	authororganization = "University of California, Los Angeles",
	copyrightholder = "authors",
}

Copyright

This paper is copyright © 1994 by its authors. Permission to make digital or hard copies of part or all of this work for personal use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that new copies bear this notice and the full citation on the first page. Abstracting with credit is permitted.

To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission of the authors.