Youhei Tanaka

Design and implementation of transactional agent

A Transactional Agent (TA) is a mobile agent to manipulate objects with some type of commitment condition. For example, a transactional agent commits only if at least one object could be successfully manipulated in the at-least-one condition. Computers may stop by fault while networks are assumed to be reliable. In the Client-Server (CS) model, servers can be fault-tolerant according to traditional replication and checkpointing technologies. However, an application program cannot be performed if a client computer is faulty. An application program can be performed on another operational computer even if a computer is faulty in the transactional agent model. There are kinds of faulty computers for a transactional agent, current, destination, and sibling computers where a transactional agent now exist, will move, and has visited, respectively. We discuss how the transactional agent can be tolerant of the types of computer faults.

A mobile agent model for fault-tolerant manipulation on distributed objects

Abstract In this paper, we discuss how to realize fault-tolerant applications on distributed objects. Servers supporting objects can be fault-tolerant by taking advantage of replication and checkpointing technologies. However, there is no discussion on how application programs being performed on clients are tolerant of clients faults. For example, servers might block in the two-phase commitment protocol due to the client fault. We newly discuss how to make application programs fault-tolerant by taking advantage of mobile agent technologies where a program can move from a computer to another computer in networks. An application program to be performed on a faulty computer can be performed on another operational computer by moving the program in the mobile agent model. In this paper, we discuss a transactional agent model where a reliable and efficient application for manipulating objects in multiple computers is realized in the mobile agent model. In the transactional agent model, only a small part of the application program named routing subagent moves around computers. A routing subagent autonomously finds a computer which to visit next. We discuss a hierarchical navigation map which computer should be visited price to another computer in a transactional agent. A routing subagent makes a decision on which computer visit for the hierarchical navigation map. Programs manipulating objects in a computer are loaded to the computer on arrival of the routing subagent in order to reduce the communication overhead. This part of the transactional agent is a manipulating subagent. The manipulation subagent still exists on the computer even after the routing subagent leaves the computer in order to hold objects until the commitment. We assume every computer may stop by fault while networks are reliable. There are kinds of faulty computers for a transactional agent; current, destination, and sibling computers where a transactional agent now exists, will move, and has visited, respectively. The types of faults are detected by neighbouring manipulation subagents by communicating with each other. If some of the manipulation subagents are faulty, the routing subagent has to be aborted. However, the routing subagent is still moving. We discuss how to efficiently deliver the abort message to the moving routing subagent. We evaluate the transactional agent model in terms of how long it takes to abort the routing subagent if some computer is faulty.

Design and implementation of transactional agents for manipulating distributed objects

A transactional agent is a mobile agent which manipulates objects distributed in computers. A transactional agent is composed of routing, manipulation, and commitment agents. A way to move to computers is decided in the routing agent. Objects in each computer are manipulated in a manipulation agent. After visiting computers, a transactional agent makes a destination on commitment by using the commitment agent. In addition, objects obtained from a computer in the manipulation agent have to be delivered to other computers where the transactional agent is performed. We discuss a model of transactional agent and implementation of a transactional agent on database servers and evaluate the transactional agents.

A fault-tolerant transactional agent model on distributed objects

A transactional agent is a mobile agent to manipulate objects distributed on computers with some type of commitment condition. For example, a transactional agent commits only if at least one object could be successfully manipulated in the at-least-one commitment condition. Computers may stop by fault while networks are assumed to be reliable. In the client-server model, servers can be fault-tolerant according to traditional replication and checkpointing technologies. However, an application program cannot be performed if a client computer is faulty. An application program can be performed on another operational computer even if a computer is faulty in the transactional agent model. For example, a transactional agent can move to another operational computer if some destination computer where the agent to move is faulty. There are kinds of faulty computers for a transactional agent, current, destination, and sibling computers where a transactional agent now exist, will move, and has visited, respectively. We discuss how the transactional agent can be tolerant of the types of faults. We show how a program reliably manipulating objects can be realized in a mobile agent in presence of computer faults

Transactional agent model for fault-tolerant object systems

A transactional agent is a mobile agent which manipulates objects in multiple computers by autonomously finding a way to visit the computers. The transactional agent commits only if its commitment condition like atomicity is satisfied in presence of faults of computers. On leaving a computer, an agent creates a surrogate agent which holds objects manipulated. A surrogate can recreate a new incarnation of the agent if the agent itself is faulty. If a destination computer is faulty, the transactional agent finds another operational computer to visit. After visiting computers, a transactional agent makes a destination on commitment according to its commitment condition. We discuss design and implementation of the transactional agent which is tolerant of computer faults.

Distributed Multimedia Streaming Systems in Peer-to-Peer Overlay Networks

A multimedia content are distributed to peers and a contents peer which holds contents can provide other peers with the contents in peer-to-peer (P2P) overlay networks. Multimedia streaming is more significant than downloading ways in multimedia applications from security and economical reasons. We discuss distributed multi-source streaming models. Here, a collection of multiple contents peers in parallel transmit packets of a multimedia content to a leaf peer to realize the reliability and scalability. Even if not only some number of peers stop by fault and are degraded in performance but also some number of packets are lost and delayed, a leaf peer can receive content at the required rate. We discuss how to allocate packets to each contents peer. We discuss a gossip-based, DAG-based coordination protocol (DCoP) to synchronize multiple contents peers. We evaluate DCoP in terms of how long it takes and how many messages are transmitted to synchronize multiple contents peers

A fault-tolerant transactional agent model on distributed object systems

A transactional agent is a mobile agent to manipulate objects distributed on computers with some commitment condition like atomic commitment. Computers may stop by fault. In the client-server model, servers can be fault-tolerant according to replication and checkpointing technologies. However, an application program cannot be performed if a client computer is faulty. A transactional agent can move to another operational computer if some destination computer to which the agent to move is faulty. In this paper, we discuss how a program reliably manipulating objects can be realized in a mobile agent in presence of computer faults.

Transactional agent on distributed objects

A transactional agent is a mobile agent to manipulate distributed objects. A transactional agent is composed of routing and manipulation subagents. After visiting computers, a routing agent makes a decision on commitment by using its commitment condition. Objects in each computer are manipulated in a manipulation agent. In addition, objects obtained from a computer have to be delivered to other computers where the transactional agent is performed. A schedule to visit computers is made from the input-output relation of manipulation agents. We discuss how to implement a transactional agent in Aglets for database servers. We evaluate the transactional agent model in terms of accessing time compared with the client-server model.

Transactional agents on distributed object systems

A transactional agent is a mobile agent to manipulate objects distributed on computers. A transactional agent can change a schedule to visit computers if some target computer is faulty. In order to reduce the communication overhead, a transactional agent is composed of routing and manipulation subagents. A routing subagent makes a decision on what computer to visit in presence of faults of computers. On arrival at the computer, the routing subagent loads classes of a manipulation subagent to locally manipulate objects. We evaluate the transactional agent model in terms of access time compared with the traditional client-server model.

Fault Detection and Recovery in a Transactional Agent Model

Servers can be fault-tolerant through replication and checkpointing technologies in the client server model. However, application programs cannot be performed and servers might block in the two-phase commitment protocol due to the client fault. In this paper, we discuss the transactional agent model to make application programs fault-tolerant by taking advantage of mobile agent technologies where a program can move from a computer to another computer in networks. Here, an application program on a faulty computer can be performed on another operational computer by moving the program. A transactional agent moves to computers where objects are locally manipulated. Objects manipulated have to be held until a transactional agent terminates. Some sibling computers which the transactional gent has visited might be faulty before the transactional agent terminates. The transactional agent has to detect faulty sibling computers and makes a decision on whether it commits/aborts or continues the computation by skipping the faulty computers depending on the commitment condition. For example, a transactional agent has to abort in the atomic commitment if a sibling computer is faulty. A transactional agent can just drop a faulty sibling computer in the at-least-one commitment. We evaluate the transactional agent model in terms of how long it takes for the transactional agent to treat faulty sibling computers .