Employment of mobile multiagent systems for attendance of transaction of distributed database

Transcription

1 Proceedings of the International Multiconference on ISSN Computer Science and Information Technology, pp PIPS Employment of mobile multiagent systems for attendance of transaction of distributed database Zofia Kruczkiewicz 1 1 The Institute of Computer Engineering, Control and Robotics, Wroclaw University of Technology, Wrocław, Poland zofia.kruczkiewicz@pwr.wroc.pl Abstract. It is aimed at the limitation of the network traffic which is generated during the realization of two-phase-commit protocol of distributed transactions in distributed database systems. This paper presents the way of the decrease of the number and the way of the diminution of the size of messages sent during distributed transactions as the manner of the limitation of the network traffic. Multiagent system is employed for attendance of confirmation of two-phase distributed transactions. The paper presents the manner of the limitation of the network traffic in multiagent systems as the use of mobile agents as resources managers of databases, static agents as coordinators of transactions and static agents as managers of transactions. These agents communicate via two-phasecommit protocols. The paper presents the performance eperiments enabling the comparison of two-phase-commit protocols, the protocol elaborated in the paper and the protocol described in the literature. 1 Introduction General applicable distributed computerized information systems store information in distributed heterogeneous databases. It is aimed at such efficient work of these systems, which generate the network traffic as small as possible. This system should have the high performance. Therefore mechanisms of the mobility and the intelligent behavior of employed software are used in these systems. The base of the maintenance of the indivisibility of realized distributed transactions of distributed heterogeneous databases, the immunity from states of the disconnection and movements of the part of systems, is the two-phase-commit protocol. It is described multiagent systems for attendance of confirmation of two-phase validation of distributed transactions in the paper. The paper presents the two-phase-commit protocol based on mobile agents, which is projected during the analyses of the MAS. This protocol includes the limited number and the least size of messages and it generates the smaller traffic than the protocol presented in the literature [13]. The concept and the implementation of activities and communication between agents play the basic role in the creation of multiagent systems (MASs). It results from the basic paradigm of MAS, which is the social character of a system i.e. the 71

2 72 Zofia Kruczkiewicz autonomy, the adaptation and interactions. The transmission of information in MASs is based on conversations [11], which include interactions and activities. These interactions and activities affect on the performance of the system and the network traffic. Performance engineering is engaged on the problems of the performance of software, during all phases of its creation. It is possible to value the performance of the system and the size of sent information in the network as time parameters of the system. Therefore it is possible to perform the choice of arbitrated solutions due to the time parameters of the model of MAS, which are matched to degree of the development of the software [1, 2]. It puts the stress on limitation of the size and the number of messages of protocols of created MASs. The mobility of software is one of the manners of this limitation, which relies on transmission of mobile agent as autonomous unit of software [6]. The mobile agent is relocated in the network of type of WAN or LAN, it decides about its activities, it eecutes services of the sending system. It is differed following patterns of interaction protocols: the static protocol (behaviors of agents and interactions are not changed) and the mobile protocol (behaviors of agents and interactions are changed). The choice of the mobility results from the type of an application and it leads to the minimization of the network traffic, the cost of CPU, generalizations of services, the autonomy of components of software, the higher immunity from errors of components moved in the network than from errors of components of the client server architecture, the elasticity of management of data and the encapsulation of the protocol. Several defined patterns of communications based on the mobility are compared in work [6]: client-server (CS, Client-Server), remote start-up of code - (REV, Remote Evaluation), transmission of code (COD, Code Demand) and mobile agent (MA, Mobile Agent). The work [4] presents methods of the improvement of the performance and the network traffic of MAS ACORN, which rely on the dynamic grouping of mobile agents in cafes due to their information and the introduction of the idea of the agent architecture as the Thick/Thin agents. The Thin agent is the mobile agent, which collects information during movement in the network and sends this information to the static agent of the type of the Thick agent. The works [3], [8] compare the performance of patterns of interaction protocols of CS and MA. It defines the sequence and parallel architecture for these patterns [8] and researches their performance in the respect of the performance of Voyager, Aglets and Concordia. The work [11] compares static and mobile MASs, which are equivalent in the respect of realized tasks. This paper describes the research of the performance of the serialization of agents as the mechanism of the mobility. The intelligent and efficient behavior of MAS enables limitation of the network traffic generated during distributed transactions of heterogeneous databases in the distributed environment. The review of systems of attendance of mobile transaction is presented in the work [12]. These systems are Clustering, Two-Tier Replication, Pro-motion, Reporting, Semi-based, Prewrite, Kangaroo Transaction, Multidatabase Transaction Processing Manager. The work [12] performs the comparison of operation models, ownership ACID, cohesions, transparency, stability, reactions on disconnect and mobility of elements of the system and it serves the proposal of the system for the attendance of the mobile transaction (MTS, Mobile Transaction Service). The work [13] presents the role of agents in improvement of the safety of distributed transactions of the system based on the technology CORBA. The work

3 Employment of mobile multiagent systems for attendance of transaction of distributed database 73 [10] describes the architecture of Distributed Database Management Systems (DBMSs), which employs the tool named CaseLP in specifying elements and testing of behavior of the system. The work [9] presents pro-active MAS, which is based on static and mobile agents which support distributed transactions of the system. These mobile agents improve the performance in comparison with classic solutions applying mobile agents. The system is realized as the platform based on IBM Aglets and the virtual machine of java (JVM) in the environment of Aglets Software Development Kit (ASDK). The second chapter of work introduces MAS JADE. It presents protocols of validation of two-phase transactions in the fourth chapter. The fifth chapter serves the results of performance eperiments concerning on comparison of two protocols i.e. the elaborated two-phase-commit protocol and the protocol presented in the work [13]. Work is ended with conclusions. 2 System MAS JADE It chooses Java MAS JADE (Java Agent Development Framework) system [7] based on FIPA specification (The Foundation for Intelligent Agents) [5] for the implementation of two-phase-commit protocols. JADE includes packages for the creation of agents and the environment of their operations as the platform of agents (AP, Agent Platform) (fig. 1). AP platform consists of following agent components: Agent Management System (AMS), which fulfils the control over the access and the utilization of agent platform; Directory Facilitator (DF), which catalogues services of applications; Message Transport System (MTS), which controls the sent messages; Agent, which represents applications. AP can be divided onto several machines as containers (fig. 1). Each container has the virtual machines of Java (JVM) and includes one or many interacting agents. The main container includes AMS and DF agents and the RMI register (Remote Method Invocation) which controls the mobility of messages and the optional mobility of agents of one AP. Containers are connected with the main container and they build the environment of operations of set of agents. According to FIPA specification, DF and AMS communicate by use of ACL (Agent Content Language) language, Fipa-Agent-Management ontology and Fipa-Request interaction protocol.

4 74 Zofia Kruczkiewicz Fig. 1. Distributed Agent platform and JADE containers [7] 3. Two-phase-commit protocols based on static and mobile agents Communication between agents is defined by the use of the interaction protocol (IP) [5]. System JADE offers the set of patterns of interaction protocols based on FIPA specification. These protocols are dedicated to different typical applications. JADE supports implementation of user-defined protocols. Patterns of protocols are placed in FIPA Interaction Protocol Library Maintenance [5]. It introduces new diagrams to design of interactions between agents, which are called protocol diagrams (PD, Protocol Diagrams). PD is based on UML sequences diagrams. It epresses new elements of PD diagrams in meta-uml language, named AUML (Agent UML) [5]. It presents IP protocols of eemplary applications at diagrams of fig.2-3. The design system consists of following elements: environments of MAS JADE, the static agent as Transaction Manager, which administers transactions, static agents as and, which gather information of eecution states of the fragments of distributed transaction and static or mobile agents as,, Manager_3 and Manager_4, which oversee eecution of fragments of distributed transaction realized in allocated resources. Agents act according to concept of Thick /Thin agent [4], i.e.: the static thick agent as Manager owns the full knowledge of its environment, it is able to acquire, to process and to analyze information therefore it has own code of a big size the mobile thin agent as Manager owns the limited knowledge of its environment and the limited range of operations, but it is able to migrate in network and it has own code of a small size. The comparison of interaction protocols bases on the assumptions that they enable realization of the same task on the same data placed on same hosts and this protocol is the best in the point of generated network traffic, which allows to eecuting task of the smallest joint size of sent messages.

5 Employment of mobile multiagent systems for attendance of transaction of distributed database 75 The IP1 protocol as two-phase-commit protocol (fig. 2) is used in the MASs presented in the work [13]. The thick agent as Manager Transaction sends a begin_transaction messages about beginning of transaction to the set of agents, which includes at least two agents i.e. and. Agents as and send messages about beginning of transaction (request_1, request_2, request_3, request_4) to static thick agents as,, Manager_3 and Manager_4. Then agents as and send can-commit message about query of the fragment of the distributed transaction to agents as,, Manager_3 and Manager_4. Each agent as Manager confirms by sending message about the correct result of the part of the transaction or failure message about the failure to the agent as Manager. After receiving all answers, agents as and send message to the agent as Transaction Manager if agents as Manager confirm all correct parts of transaction or failure message, if at least the one agent as Manager reports the failure. If the agent as Transaction Manager receives messages from all agents as Manager, it sends messages to them about the commit of the distributed transaction, in the opposite case if it receives at least one failure message, it sends messages to all agents as Manager about the come-back of the state of resources before the beginning of the transaction. In the first case agents as Managers send messages to all agents as Manager. Net agents as Manager confirm by sending have-commit messages to agents as s Manager which send have-commit messages to the agent as Transaction Manager. In the second case agents as Manager send messages to agents as Manager. Agents as Resource Manager confirm the failure of the transaction by sending have- messages to agents as Manager. Net agents as s Manager send have- messages to the agent as Transaction Manager about confirmation of the failure of the transaction. The protocol IP2 at the figure 3 differs from protocol IP1 at the figure 2 where two mobile thin agents are employed in overseeing resources of transaction. Instead of request and can-commit messages it is sent request-to-move messages with information of network migrations which are necessary for the eecution of fragments of the transaction. Protocol IP2 does not include four can-commit messages, because mobile agents as and must not receive them however the network traffic appears when the mobile agents as Managers migrate through network and eecute all fragments of the transaction. The time of the realization of request to move (request_1, request_2) message consists of the time of the receiving this message by mobile agent as and two migrations to databases placed on computers of net addresses given by parameters request_1 and request _2. The agent as sends ok commit or failure message after realization of fragments of transactions in two databases to the agent as which sends ok commit or failure message to the agent as Transaction Manager. During the second phase of transaction the agent as

6 76 Zofia Kruczkiewicz receives do_commit or message and it sends one of these messages to the agent as. It migrates through two databases and commits or cancels the fragments of the transaction. Then it sends have commit or have message to the agent as. The agent as sends have commit or have message to the agent as Transaction Manager. The same conditions concern the agent as. The smaller network traffic is generated when the eecuting of the fragment of transaction fails during the first migration. The agent as and finishes the eecuting of the transaction without another migration and sends failure message to own agent as Manager. During the second phase of the transaction it migrates to the first database and cancels the state of its resources. It decreases the number of migrations of agents from eight to four. In general, the protocol with mobile agents includes n agents as Managers and each agent as Manager coordinates p agents as Manager and each agent as Manager migrates through q databases. The number q is greater than 1. The epression p*q is equal to the number of agents as Manager of IP1 protocol. It is taken the assumption that the size of all messages and the size of code of the each mobile agent are equal to a. Therefore the IP1 protocol includes the number of messages which is equal to the value of the following epression: (4*n + 5*n*p*q)* a. The IP2 protocol includes the number of messages which is equal to the following epression: (4*n + 4*n*p+2*n*p*q)* a. The difference between these epressions is equals to value: n*p*(3*q 4)*a. It means that the IP1 protocol has the greater joint size of messages than IP2 protocol. If the transaction of IP2 protocols fails during the first migration of the each mobile agent, its epression is equal to the following one: (4*n + 6*n*p)* a. Now the difference between two epressions is equal to n*p*(5*q-6) and it is greater than the first difference. The IP2 protocol can generate the smaller network traffic than the IP1 one. 4 Performance eperiments It constructs equivalent static and mobile MASs due to the number of databases. MASs are based on IP1 and IP2 interaction protocols (fig. 2, fig. 3). Researching of the time of the answer is purpose of the eperiment in comparison with the generated network traffic of the static and the mobile MASs i.e. the time that epires from the moment of the beginning of the task of searching out to the time of receiving the result of searching. The system based on thick agents of IP1 interaction protocol is presented on fig. 4 and system based on mobility thin agents based of IP2 interaction

7 Employment of mobile multiagent systems for attendance of transaction of distributed database 77 Transaction Manager begin-transaction (task) begin-transaction (task) request_1 request_2 can-commit can-commit Manager_3 Manager_4 request_3 request_4 can-commit can-commit Phase 1 Phase 2 Meta-UML symbols have been used during sending messages - - decision type: one from many - parallel type: AND Fig. 2. IP1 protocol of validation of two phase distributed transaction of MAS based on static agents [13]

8 78 Zofia Kruczkiewicz Transaction Manager begin-transaction (task) begin-transaction (task) request-to-move(request_1, request_2) request-to-move(request_3, request_4) Phase 1 Phase 2 Meta-UML symbols have been used during sending messages - - decision type: one from many - parallel type: AND Fig. 3. IP2 protocol of validation of two phase distributed transaction of MAS based on static and mobile agents protocol is presented on fig. 5. Technical data of MASs are presented in tab.1. It carries research on computers of the local network acting on 100BASE-TX. The agent is independent thread of virtual java machine (JVM) in system acting on JADE i.e. the independent thread of operating system, which works under control of JADE. Each agent can eecute several independent tasks simultaneously. In order to build detached threads for the each agent, it introduces the concept of the behavior. This solution is efficient, because the transfer of the steering from the thread to the thread is hundred times slower than the calling method each agent behavior is called

9 Employment of mobile multiagent systems for attendance of transaction of distributed database 79 by the agent method [7]. Communication and mobility of agents are based on RMI of JAVA, which employs the migration of the code and the state of agents. Host2, Container1 Host1, MainContainer Transaction Manager Host3, Container2 Request of data 10 MB Result Request of data 10 MB Result 100 MB LAN 128 K 10MB 10MB 128 K Host4, Container3 MS SQL Server Host5, Container4 MYSQL Host6, Container4 Manager_3 MS SQL Server Host7, Container6 Manager_4 MYSQL Fig. 4. Analysis of communication infrastructure system in the following environment: seven hosts, static solution based on IP1 Host2, Container1 Agent_1 Agent_1 Host1, MainContainer Transaction Manager Host3, Container2 Agent_2 Agent_2 Request move for data 10 MB Result 100 MB LAN Request move for data 10 MB Result 128 K 10MB 10MB 128 K Host4, Container3 MS SQL Server Host5, Container5 MYSQL Host6, Container4 MS SQL Server Host7, Container6 MYSQL Fig. 5. Interaction infrastructure of MAS in the following environment: seven hosts, system IP2 Evaluated systems are researched without taking into consideration influence of the graphic interface of user. Agents as Manager eecute task of searching out on servers of databases systems MySQL and MSQL Server 2000, with database of bookstore. Each of table stores 1000 records of data of clients of bookstores. Static and mobile agents as Manager eecute the SQL query: SELECT * FROM klienci WHERE nazwisko LIKE 'X%'. Realized query is not a transaction but this solution enables to evaluate the influence of IP1 and IP2 protocols on performance of two-phase distributed transactions. The time of each searching is gauged by the use of the java class method i.e. System.currentTimeMillis.

10 80 Zofia Kruczkiewicz Tab. 1. Technical test machines data Hosts 1, 2 Hosts 3, 4, 5, 7 OS MS Windows 2000 MS Windows XP CPU Celeron 1GHz Athlon XP RAM 120 MB 256 MB JVM Sun SDK 1.5 Sun JRE 1.5 JADE Tab. 2. Time [ms] of searching of MASs after 1000 tests on 7 computers Time [ms] MAS based on IP1MAS based on IP2 Average time Ma time Min time In the static solution each query is repeated for 250 times by each Manager. In the mobile solution each Manager migrates between two hosts for 250 times per the one host. The operation of the static agent is equivalent to the one migration of the mobile agent. It presents results of research in table 2.The group of mobile agents is faster than the group of static agents. This improvement of the performance of IP2 protocols results from the limited number of mobile agents and the smaller size of its code than the size of message sending to static agents. 5 Conclusions After the employment of the proper pattern of interaction protocol based on mobility it is possible to ascertain the mobility solution on the base of carried performance tests of MASs. This solution can eceed stationary solution in respect of: higher performance - MAS based on IP2 interaction protocol with the mobility acts faster than the equivalent static solutions based on IP1 interaction protocol small capacity of software the capacity of the mobile test configuration of MAS based on IP2 protocol is less than for the static solution based on IP1 protocol small network traffic - it is possible to employ the simplest interaction protocol at the configuration of the agent according to the concept of Thick /Thin agent, where the thin agent is mobile.

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