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Data Consistency in Intermittently Connected Distributed Systems
November/December 1999 (vol. 11 no. 6)
pp. 896-915

Abstract—Mobile computing introduces a new form of distributed computation in which communication is most often intermittent, low-bandwidth, or expensive, thus providing only weak connectivity. In this paper, we present a replication scheme tailored for such environments. Bounded inconsistency is defined by allowing controlled deviation among copies located at weakly connected sites. A dual database interface is proposed that in addition to read and write operations with the usual semantics supports weak read and write operations. In contrast to the usual read and write operations that read consistent values and perform permanent updates, weak operations access only local and potentially inconsistent copies and perform updates that are only conditionally committed. Exploiting weak operations supports disconnected operation since mobile clients can employ them to continue to operate even while disconnected. The extended database interface coupled with bounded inconsistency offers a flexible mechanism for adapting replica consistency to the networking conditions by appropriately balancing the use of weak and normal operations. Adjusting the degree of divergence among copies provides additional support for adaptivity. We present transaction-oriented correctness criteria for the proposed schemes, introduce corresponding serializability-based methods, and outline protocols for their implementation. Then, some practical examples of their applicability are provided. The performance of the scheme is evaluated for a range of networking conditions and varying percentages of weak transactions by using an analytical model developed for this purpose.

[1] R. Alonso, D. Barbara, and H. Garcia-Molina, "Data Caching Issues in an Information Retrieval System," ACM Trans. Database Systems, vol. 15, no. 3, pp. 359-384, Sept. 1990.
[2] D. Barbará and H. Garcia-Molina, "Replicated Data Management in Mobile Environments: Anything New Under the Sun?" Proc. IFIP WG10.3 Working Conf. Applications in Parallel and Distributed Computing,Caracas, Venezuela, Apr. 1994.
[3] P. Bernstein, V. Hadzilacos, and N. Goodman, Concurrency Control and Recovery in Database Systems. Addison-Wesley, 1987.
[4] D. Bertzekas and R. Gallager, Data Networks, second ed. Prentice-Hall, 1992.
[5] S.B. Davidson, H. Garcia-Molina, and D. Skeen, "Consistency in Partitioned Networks," ACM Computing Surveys, vol. 17, no. 3, pp. 341-370, Sept. 1985.
[6] A. Demers, K. Pertersen, M. Spreitzer, D. Terry, M. Theier, and B. Welch, “The Bayou Architecture: Support for Data Sharing among Mobile Users,” IEEE Proc. Workshop Mobile Computing Systems and Applications, Dec. 1994.
[7] G.H. Forman and J. Zahorjan, “The Challenges of Mobile Computing,” Computer, pp. 38-47, Apr. 1994.
[8] H. Garcia-Molina and G. Wiederhold, Read-Only Transactions in a Distributed Database System ACM Trans. Database Systems, vol. 7, no. 2, pp. 209-234, June 1982.
[9] J. Gray, P. Helland, P. O'Neil, and D. Shasha, “The Dangers of Replication and a Solution,” Proc. 1996 ACM SIGMOD Conf. Management of Data, SIGMOD Record, pp. 173-182, June 1996.
[10] P. Honeyman and L.B. Huston, “Communications and Consistency in Mobile File Systems,” IEEE Personal Comm., Dec. 1995.
[11] Y. Huang, P. Sistla, and O. Wolfson, "Data Replication for Mobile Computers," Proc. ACM-SIGMOD Int'l Conf. Management of Data,Minneapolis, Minn., May 1994.
[12] L.B. Huston and P. Honeyman, “Partially Connected Operation,” Computing Systems, vol. 4, no. 8, Fall 1995.
[13] T. Imielinski and B.R. Badrinath, “Wireless Computing: Challenges in Data Management,” Comm. ACM, vol. 37, no. 10, Oct. 1994.
[14] J.J. Kistler and M. Satyanarayanan, "Disconnected Operation in the Coda File System," ACM Trans. Computer Systems, vol. 10, no. 1, Feb. 1992, pp. 3-25.
[15] N. Krishnakumar and A.J. Bernstein, "Bounded Ignorance: A Technique for Increasing Concurrency in a Replicated System," ACM Trans. Database Systems, vol. 19, no. 4, pp. 586-625, Dec. 1994.
[16] N. Krishnakumar and R. Jain, “Protocols for Maintaining Inventory Databases and User Profiles in Mobile Sales Applications,“ Proc. Mobidata Workshop, Oct. 1994.
[17] Q. Lu and M. Satyanarayanan, “Improving Data Consistency in Mobile Computing Using Isolation-Only Transactions,” Proc. Fifth IEEE HotOS Topics Workshop, May 1995.
[18] Q. Lu and M. Satyanarayanan, “Resource Conservation in a Mobile Transaction System,” IEEE Trans. Computers, vol. 46 no. 3, Mar. 1997.
[19] K. Miller, “Cellular Essentials for Wireless Data Transmission,” Data Comm., vol. 23, no. 5, pp. 61–67, Mar. 1994.
[20] L. Mummert, M. Ebling, and M. Satyanarayanan, "Exploiting Weak Connectivity for Mobile File Access," Proc. 15th ACM Symp. Operating Systems Principles, pp. 143-155, Dec. 1995.
[21] B.D. Noble, M. Price, and M. Satyanarayanan, “A Programming Interface for Application-Aware Adaptation in Mobile Computing,” Computing Systems, vol. 8, no. 4, Winter 1996.
[22] C. Papadimitriou, The Theory of Database Concurrency Control. Computer Science Press, 1986.
[23] K. Patersen, M.J. Spreitzer, D.B. Terry, M.M. Theimer, and A.J. Demers, “Flexible Update Propagation for Weakly Consistent Replication,” Proc. 16th ACM Symp. Operating Systems Principles, Oct. 1997.
[24] E. Pitoura, “A Replication Schema to Support Weak Connectivity in Mobile Information Systems,” Proc. Seventh Int'l Conf. Database and Expert Systems Applications (DEXA), Sept. 1996.
[25] E. Pitoura and B. Bhargava, “Building Information Systems for Mobile Environments,” Proc. Third Int'l Conf. Information and Knowledge Management, pp. 371-378, Nov. 1994.
[26] E. Pitoura and B. Bhargava, “Maintaining Consistency of Data in Mobile Distributed Environments,” Proc. 15th Int'l Conf. Distributed Computing Systems, 1995.
[27] E. Pitoura and G. Samaras, Data Management for Mobile Computing. Kluwer Academic, 1997.
[28] C. Pu and A. Leff, "Replica Control in Distributed Systems: An Asynchronous Approach," Proc. ACM SIGMOD Int'l Conf. Management Data, pp. 377-386, 1991.
[29] K. Ramamrithan and C. Pu, "A Formal Characterization of Epsilon-Serializability," IEEE Trans. Knowledge and Data Eng., vol. 7, no. 6, pp. 997-1,007, Dec. 1995.
[30] M. Satyanarayanan, J.J. Kistler, L.B. Mummert, M.R. Ebling, P. Kumar, and Q. Lu, “Experience with Disconnected Operation in a Mobile Comp uting Environment,” Proc. 1993 Usenix Symp. Mobile and Location-Independent Computing, Aug. 1993.
[31] A. Sheth and M. Rusinkiewicz, "Management of Interdependent Data: Specifying Dependency and Consistency Requirements," Proc. Workshop Management Replicated Data, pp. 133-136, 1990.
[32] C. Tait and D. Duchamp, "Service Interface and Replica Management Algorithm for Mobile File System Clients," First Int'l Conf. Parallel and Distributed Information Systems,Miami Beach Fla., pp. 190-197, Dec. 1991.
[33] C.D. Tait and D. Duchamp, “An Efficient Variable-Consistency Replicated File Service,” Proc. Usenix File Systems Workshop, pp. 111–126, May 1992.
[34] H. Takagi, Queueing Analysis, Vol. 1: Vacation and Priority Systems. North-Holland, 1991.
[35] D. Terry, A. Demers, K. Petersen, M. Spreitzer, M. Theimer, and B. Welch, Session Guarantees for Weakly Consistent Replicated Data Proc. Int'l Conf. Parallel and Distributed Information Systems, pp. 140-149, Sept. 1994.
[36] D.B. Terry, M.M. Theimer, K. Petersen, A.J. Demers, M.J. Spreitzer, and C.H. Hauser, Managing Update Conflicts in a Weakly Connected Replicated Storage System Proc. ACM Symp. Operating Systems Principles, 1995.
[37] D.G. Walborn and P.K. Chrysanthis, “Supporting Semantics Based Transaction Processing in Mobile Database Applications,” Proc. 14th IEEE Symp. Reliable Distributed Systems, Sept. 1995.
[38] M. Wong and D. Agrawal, "Tolerating Bounded Inconsistency for Increasing Concurrency in Database Systems," Proc. 11th Principles of Database Systems, pp. 236-245, 1992.
[39] P.S. Yu, D.M. Dias, and S.S. Lavenberg, "On the Analytical Modeling of Database Concurrency Control," J. ACM, vol. 40, no. 4, pp. 831-872, Sept. 1993.

Index Terms:
Mobile computing, concurrency control, replication, consistency, disconnected operation, transaction management, adaptability.
Evaggelia Pitoura, Bharat Bhargava, "Data Consistency in Intermittently Connected Distributed Systems," IEEE Transactions on Knowledge and Data Engineering, vol. 11, no. 6, pp. 896-915, Nov.-Dec. 1999, doi:10.1109/69.824602
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