1 Logical Clock based Last Update Consistency Model for Distributed Shared Memory Rubaiyat Rafat Institute of Information Technology University of Dhaka Dhaka, Bangladesh Email: rubaiyat rafat@yahoo.com Kazi Sakib Institute of Information Technology University of Dhaka Dhaka, Bangladesh Email: sakib@univdhaka.edu Abstract—Excessive locking and cumulative up- dates in Distributed Shared Memory (DSM) not only reduces the parallelism for block access but also causes a serious degradation in response time for a dense network. This paper proposes a new consis- tency model in DSM named Last Update Consistency (LUC) model, where the model uses logical clock counter to keep the DSM consistent. The logical clock always increases never decreases. So the increasing order of the logical clock value is used to provide the request to the DSM. In this model, multiple nodes can perform READ operations over the same block at a time. For WRITE operation over the same block, only the last modification will exist and the earlier WRITE operations will be treated as obsolete WRITE and should be discarded. The experimental and analytical analysis showed that the proposed model effectively reduces the unnecessary network traffic and cumulative block updates that exist in the Sequential Consistency Model and Release Consistency Model. Index Terms—Distributed Shared Memory, Shared Memory, TimeStamp Protocol, Consistency Model, Distributed System. I. I NTRODUCTION Increasing network density invokes the scalabil- ity issue for DSM. When large number of nodes exists in the distributed system, regular broadcast of block modification not only degrades the perfor- mance of DSM but also abuse the network traffic of the system. Cumulative block modification is another factor that degrades the performance of DSM and becomes a threat for the existing limited storage structure [11]. When a DSM model provides more concentration on sequential consistency, parallelism is reduced as a trade off. For maintaining consistency, one phase locking and two phases locking (SHARED and EXCLUSIVE) protocol [2] have been used by