A DMVOCC-MVDA(distributed multiversion optimistic concurrency control with multiversion dynamic adjustment)protocol was presented to process mobile distributed real-time transaction in mobile broadcast environments.At...A DMVOCC-MVDA(distributed multiversion optimistic concurrency control with multiversion dynamic adjustment)protocol was presented to process mobile distributed real-time transaction in mobile broadcast environments.At the mobile hosts,all transactions perform local pre-validation.The local pre-validation process is carried out against the committed transactions at the server in the last broadcast cycle.Transactions that survive in local pre-validation must be submitted to the server for local final validation.The new protocol eliminates conflicts between mobile read-only and mobile update transactions,and resolves data conflicts flexibly by using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions.Mobile read-only transactions can be committed with no-blocking,and respond time of mobile read-only transactions is greatly shortened.The tolerance of mobile transactions of disconnections from the broadcast channel is increased.In global validation mobile distributed transactions have to do check to ensure distributed serializability in all participants.The simulation results show that the new concurrency control protocol proposed offers better performance than other protocols in terms of miss rate,restart rate,commit rate.Under high work load(think time is 1s)the miss rate of DMVOCC-MVDA is only 14.6%,is significantly lower than that of other protocols.The restart rate of DMVOCC-MVDA is only 32.3%,showing that DMVOCC-MVDA can effectively reduce the restart rate of mobile transactions.And the commit rate of DMVOCC-MVDA is up to 61.2%,which is obviously higher than that of other protocols.展开更多
Recovery performance in the event of failures is very important for distributed real-time database systems. This paper presents a time-cognizant logging-based crash recovery scheme （TCLCRS） that aims at distributed ...Recovery performance in the event of failures is very important for distributed real-time database systems. This paper presents a time-cognizant logging-based crash recovery scheme （TCLCRS） that aims at distributed real-time databases, which adopts a main memory database as its ground support. In our scheme, each site maintains a real-time log for local transactions and the subtransactions, which execute at the site, and execte local checkpointing independently. Log records are stored in non-volatile high- speed store, which is divided into four different partitions based on transaction classes. During restart recovery after a site crash, partitioned crash recovery strategy is adopted to ensure that the site can be brought up before the entire local secondary database is reloaded in main memory. The partitioned crash recovery strategy not only guarantees the internal consistency to be recovered, but also guarantee the temporal consistency and recovery of the sates of physical world influenced by uncommitted transactions. Combined with two- phase commit protocol, TCLCRS can guarantee failure atomicity of distributed real-time transactions.展开更多
In order to design a new kind of mobile database management system (DBMS)more suitable for mobile computing than the existent DBMS, the essence of database systems in mobilecomputing is analyzed. An opinion is introdu...In order to design a new kind of mobile database management system (DBMS)more suitable for mobile computing than the existent DBMS, the essence of database systems in mobilecomputing is analyzed. An opinion is introduced that the mobile database is a kind of dynamicdistributed database, and the concept of virtual servers to translate the clients' mobility to theservers' mobility is proposed. Based on these opinions, a kind of architecture of mobile DBMS, whichis of versatility, is presented. The architecture is composed of a virtual server and a local DBMS,the virtual server is the kernel of the architecture and its functions are described. Eventually,the server kernel of a mobile DBMS prototype is illustrated.展开更多
Techniques for mining information from distributed data sources accessible over the Internet are a growing area of research.The mobile Agent paradigm opens a new door for distributed data mining and knowledge discover...Techniques for mining information from distributed data sources accessible over the Internet are a growing area of research.The mobile Agent paradigm opens a new door for distributed data mining and knowledge discovery applications.In this paper we present the design of a mobile agent system which couples service discovery,using a logical language based application programming interface,and database access.Combining mobility with database access provides a means to create more efficient data mining applications.The processing of data is moved to network wide data locations instead of the traditional approach of bringing huge amount of data to the processing location.Our proposal aims at implementing system tools that will enable intelligent mobile Agents to roam the Internet searching for distributed data services.Agents access the data,discover patterns,extract useful information from facts recorded in the databases,then communicate local results back to the user.The user then generates a global data model through the aggregation of results provided by all Agents.This overcomes barriers posed by network congestion,poor security,and unreliability.展开更多
In this paper, we consider skyline queries in a mobile and distributed environment, where data objects are distributed in some sites （database servers） which are interconnected through a high-speed wired network, an...In this paper, we consider skyline queries in a mobile and distributed environment, where data objects are distributed in some sites （database servers） which are interconnected through a high-speed wired network, and queries are issued by mobile units （laptop, cell phone, etc.） which access the data objects of database servers by wireless channels. The inherent properties of mobile computing environment such as mobility, limited wireless bandwidth, frequent disconnection, make skyline queries more complicated. We show how to efficiently perform distributed skyline queries in a mobile environment and propose a skyline query processing approach, called efficient distributed skyline based on mobile computing （EDS-MC）. In EDS-MC, a distributed skyline query is decomposed into five processing phases and each phase is elaborately designed in order to reduce the network communication, network delay and query response time. We conduct extensive experiments in a simulated mobile database system, and the experimental results demonstrate the superiority of EDS-MC over other skyline query processing techniques on mobile computing.展开更多
基金Project(20030533011)supported by the National Research Foundation for the Doctoral Program of Higher Education of China
文摘A DMVOCC-MVDA(distributed multiversion optimistic concurrency control with multiversion dynamic adjustment)protocol was presented to process mobile distributed real-time transaction in mobile broadcast environments.At the mobile hosts,all transactions perform local pre-validation.The local pre-validation process is carried out against the committed transactions at the server in the last broadcast cycle.Transactions that survive in local pre-validation must be submitted to the server for local final validation.The new protocol eliminates conflicts between mobile read-only and mobile update transactions,and resolves data conflicts flexibly by using multiversion dynamic adjustment of serialization order to avoid unnecessary restarts of transactions.Mobile read-only transactions can be committed with no-blocking,and respond time of mobile read-only transactions is greatly shortened.The tolerance of mobile transactions of disconnections from the broadcast channel is increased.In global validation mobile distributed transactions have to do check to ensure distributed serializability in all participants.The simulation results show that the new concurrency control protocol proposed offers better performance than other protocols in terms of miss rate,restart rate,commit rate.Under high work load(think time is 1s)the miss rate of DMVOCC-MVDA is only 14.6%,is significantly lower than that of other protocols.The restart rate of DMVOCC-MVDA is only 32.3%,showing that DMVOCC-MVDA can effectively reduce the restart rate of mobile transactions.And the commit rate of DMVOCC-MVDA is up to 61.2%,which is obviously higher than that of other protocols.
基金Project supported by National Natural Science Foundation ofChina (Grant No .60203017) Defense Pre-research Projectof the"Tenth Five-Year-Plan"of China (Grant No .413150403)
文摘Recovery performance in the event of failures is very important for distributed real-time database systems. This paper presents a time-cognizant logging-based crash recovery scheme （TCLCRS） that aims at distributed real-time databases, which adopts a main memory database as its ground support. In our scheme, each site maintains a real-time log for local transactions and the subtransactions, which execute at the site, and execte local checkpointing independently. Log records are stored in non-volatile high- speed store, which is divided into four different partitions based on transaction classes. During restart recovery after a site crash, partitioned crash recovery strategy is adopted to ensure that the site can be brought up before the entire local secondary database is reloaded in main memory. The partitioned crash recovery strategy not only guarantees the internal consistency to be recovered, but also guarantee the temporal consistency and recovery of the sates of physical world influenced by uncommitted transactions. Combined with two- phase commit protocol, TCLCRS can guarantee failure atomicity of distributed real-time transactions.
文摘In order to design a new kind of mobile database management system (DBMS)more suitable for mobile computing than the existent DBMS, the essence of database systems in mobilecomputing is analyzed. An opinion is introduced that the mobile database is a kind of dynamicdistributed database, and the concept of virtual servers to translate the clients' mobility to theservers' mobility is proposed. Based on these opinions, a kind of architecture of mobile DBMS, whichis of versatility, is presented. The architecture is composed of a virtual server and a local DBMS,the virtual server is the kernel of the architecture and its functions are described. Eventually,the server kernel of a mobile DBMS prototype is illustrated.
文摘Techniques for mining information from distributed data sources accessible over the Internet are a growing area of research.The mobile Agent paradigm opens a new door for distributed data mining and knowledge discovery applications.In this paper we present the design of a mobile agent system which couples service discovery,using a logical language based application programming interface,and database access.Combining mobility with database access provides a means to create more efficient data mining applications.The processing of data is moved to network wide data locations instead of the traditional approach of bringing huge amount of data to the processing location.Our proposal aims at implementing system tools that will enable intelligent mobile Agents to roam the Internet searching for distributed data services.Agents access the data,discover patterns,extract useful information from facts recorded in the databases,then communicate local results back to the user.The user then generates a global data model through the aggregation of results provided by all Agents.This overcomes barriers posed by network congestion,poor security,and unreliability.
基金supported by the Natural Science Foundation of Tianjin under Grant No. 08JCYBJC12400the Innovative Foundation of Small and Medium Enterprises under Grant No. 08ZXCXGX15000+1 种基金the National High-Technology Research and Development 863 Program of China under Grant No. 2009AA01Z152the National Natural Science Foundation of China under Grant No. 60872064
文摘In this paper, we consider skyline queries in a mobile and distributed environment, where data objects are distributed in some sites （database servers） which are interconnected through a high-speed wired network, and queries are issued by mobile units （laptop, cell phone, etc.） which access the data objects of database servers by wireless channels. The inherent properties of mobile computing environment such as mobility, limited wireless bandwidth, frequent disconnection, make skyline queries more complicated. We show how to efficiently perform distributed skyline queries in a mobile environment and propose a skyline query processing approach, called efficient distributed skyline based on mobile computing （EDS-MC）. In EDS-MC, a distributed skyline query is decomposed into five processing phases and each phase is elaborately designed in order to reduce the network communication, network delay and query response time. We conduct extensive experiments in a simulated mobile database system, and the experimental results demonstrate the superiority of EDS-MC over other skyline query processing techniques on mobile computing.
