Shigenari Nakamura

Energy-Efficient Replication and Migration of Processes in a Cluster

Application processes have to be efficiently performed in presence of server faults in a cluster. Multiple replicas of a process are performed on multiple servers. However, the more number of replicas of a process are performed, the more reliable and available the process can be performed but the more amount of electric energy is consumed. In this paper, we take a process migration (MG) approach to energy efficiently and reliably performing multiple replicas of an application process on servers. A replica of a process performed on a current server st migrates to another server su if the server su is expected to consume a smaller amount of electric energy to perform the replica than the current server st while the deadline constraint of the process is satisfied. We consider synchronous and asynchronous ways for process replicas to migrate to servers. In the synchronous migration, every replica migrates to another server on a same computation state. In the asynchronous migration, each replica makes a decision on when the replica migrates to which server.

A read-write abortion protocol to prevent illegal information flow in role-based access control systems

In information systems, a transaction may illegally read data stored in an object which the transaction is not allowed to read is stored in the object. A transaction illegally writes data to an object after issuing illegal read. A transaction suspiciously reads data in a suspicious object whose data is not allowed to flow to some object. A transaction impossibly writes data to an object after issuing suspicious read. In our previous studies, the write-abortion (WA) role-based synchronisation (RBS) and object-based synchronisation (OBS) protocols are proposed where a transaction illegally or impossibly writes data to objects is aborted. In this paper, we newly propose a pair of read-write-abortion (RWA) RBS and OBS protocols where a transaction is aborted only if the transaction issues an illegal read or impossible write to an object. In the evaluation, the execution time of each transaction in RWA protocols is shorter than the WA protocols.

Role-Based Information Flow Control Models

In information systems, data in an object may illegally flow into another object if a subject manipulates the objects. In this paper, we discuss information flow control models to prevent illegal information to occur in the role-based access control (RBAC) model. First, we define a legal information flow relation ri⇒ rj among roles ri and rj. It means, if a subject granted the role ri manipulates objects before another subject granted the role rj, no illegal information flow occur. We discuss safe systems where no illegal information flow occur even if operations from different subjects are performed in any order. Then, we discuss a role-based synchronization (RBS) protocol and an object-based synchronization (OBS) protocol to prevent illegal information flow in unsafe systems. Here, a transaction is aborted if the transaction reads an object and illegal information flow might occur. In the RBS protocol, the illegal information flow condition is specified in terms of roles while objects in the OBS protocol. We evaluate the RBS and OBS protocols in terms of number of transactions aborted.

Read-abortion (RA) based synchronization protocols to prevent illegal information flow

In information systems, data in an object may illegally flow into another object through manipulations of the objects. First, we define a legal information flow relation r i ? r j among roles r i and r j . It means, if a subject granted the role r i manipulates objects before another subject granted the role r j , no illegal information flow occur. We discuss safe systems where no illegal information flow occur even if operations from different subjects are performed in any order. Then, we discuss a read-abortion role-based synchronization (RA-RBS) protocol and a read-abortion object-based synchronization (RA-OBS) protocol to prevent illegal information flow in unsafe systems. Here, a transaction is aborted if the transaction reads an object and illegal information flow might occur. We evaluate the RA-RBS and RA-OBS protocols in terms of number of transactions aborted. We propose RA-RBS and RA-OBS protocols.More than half of read operations are illegal without information flow control.No illegal information flow occur but some transactions are aborted in the protocols.The abortion ratio in the RA-OBS protocol is smaller than the RA-RBS protocol.

Simple Energy-Aware Algorithms for Selecting a Server in a Scalable Cluster

It is critical to reduce the electric energy consumed in server clusters in order to realize eco society. In our previous studies, a server is selected to perform a process by estimating the termination time of every current process and then the electric energy consumption of servers. However, it is not easy and takes time to collect the state of each process and estimate the termination time of each process. In this paper, we propose SLEA (simple locally energy-aware) and SGEA (simple globally energy-aware) algorithms to select a server where only the number of processes on each server is used. In the evaluation, we show the electric energy consumption and active time of the servers and the average execution time of processes can be reduced in the SLEA and SGEA algorithms.

Synchronization Protocols to Prevent Illegal Information Flow in Role-Based Access Control Systems

In information systems, data in an object may illegally flow into another object if transactions manipulate the objects. In our previous studies, the role-based synchronization (RBS) and object-based synchronization (OBS) protocols are discussed to present illegal information flow in the role-based access control (RBAC) model. Illegal read operations mean read operations which might imply illegal information flow. Transactions which issue illegal read operations are aborted. In this paper, we consider a unique object whose data is not allowed to flow to another object. An illegal write is defined to be a write operation which is issued after reading a unique object or illegally reading an object in a transaction. Each transaction reads any object but is aborted if the transaction illegally writes an object. Synchronization protocol WA-RBS and WA-OBS are discussed based on abortion of transaction issuing illegal write operations.

Read-Write Abortion (RWA) Based Synchronization Protocols to Prevent Illegal Information Flow

In information systems, data in an object may illegally flow into another object if transactions read and write the objects. A transaction illegally reads an object if data in objects which the transaction is not allowed to read are stored in the object. In addition, it is specified data in which object is allowed to flow to other objects. A suspicious object is an object which is not allowed to flow to some object. A transaction suspiciously reads an object if the object is suspicious. If a transaction T writes an object oj after suspiciously reading an object oi, data in the object oi might flow to the object oj. Here, if information flow from the object oi to the object oj is not allowed, the transaction T impossibly writes the object oi. In our previous studies, the read-abortion (RA) role-based synchronization (RA-RBS) and object-based synchronization (RA-OBS) protocols are discussed where a transaction is aborted if the transaction illegally reads an object. Write-abortion (WA) based protocols WA-RBS and WA-OBS are also proposed based on abortion of transactions illegally and impossibly writing objects in our previous studies. In this paper, we newly propose RWA-RBS and RWA-OBS protocols where a transaction is aborted if the transaction illegally reads an object or impossibly writes an object. We evaluate the RWA-RBS and RWA-OBS protocols in terms of number of transactions aborted. We show the smallest number of transactions are aborted in the WA types of protocols.

A Flexible Read-Write Abortion Protocol to Prevent Illegal Information Flow

Information systems have to be secure in presence of illegal access. A transaction illegally reads an object if the transaction reads the object which includes data in other objects which is not allowed to be read. A transaction illegally writes an object after illegally reading some object. In addition, we consider suspicious object whose data is not allowed to flow to another object. A transaction suspiciously reads a suspicious object. A transaction impossibly writes an object after reading a suspicious object. Write-abortion (WA) and read-write abortion (RWA) protocols to prevent illegal information flow are already discussed. In the WA protocol, a transaction is aborted once issuing an illegal or impossible write. Reads are meaninglessly performed since the reads are undone due to the abortion of the transaction. In the RWA protocol, a transaction is aborted once issuing an illegal read or impossible write. Here, read operations to be performed after an illegal read are lost since a transaction is aborted just on issuing an illegal read. In this paper, we newly propose a flexible read-write abortion (FRWA) protocol to reduce the number of meaningless and lost reads. Here, a transaction is aborted with some probability if the transaction illegally reads an object. We evaluate the FRWA protocols compared with the WA and RWA protocols. We show the execution time of each transaction in the FRWA protocols is shorter than the WA and more number of reads can be performed in the RWA protocols.

An energy-efficient process migration approach to reducing electric energy consumption in a cluster of servers

In order to realise eco society, we have to reduce electric energy consumed by servers in a cluster. Clients issue requests of application processes to servers in a cluster. Here, application processes have to be efficiently performed on servers with respect to not only performance but also energy consumption. In this paper, we newly propose an energy-efficient process migration EMG approach to energy-efficiently performing application processes on servers. Here, processes on servers migrate to other servers so that the processes are more efficiently performed. We first discuss how to estimate the termination time of each current process on a server and the total electric energy consumption of a server to perform every current process. A process performed on a current server migrates to another server if the server is expected to consume smaller electric energy to perform the process than the current server and the deadline constraint on the process is satisfied on the server by using the estimation models. In the evaluation, we show the total energy consumption of servers is smaller and the average execution time of each process is shorter in the EMG algorithm than non-migration algorithms like the round robin and random algorithms.

A Flexible Read-Write Abortion Protocol with Sensitivity of Objects to Prevent Illegal Information Flow

In information systems, objects have to be not only legally accessed in presence of illegal accesses but also data in a suspicious object is not allowed to flow to another object. A transaction illegally and suspiciously reads an object if the transaction reads the object which includes data in other objects which are not allowed to be read and the object which is suspicious, respectively. A transaction illegally and impossibly writes an object after illegally and suspiciously reading an object, respectively. The write-abortion (WA), read-write-abortion (RWA), and flexible RWA (FRWA) protocols to prevent illegal information flow are proposed in our previous papers. In the WA and RWA protocols, a transaction is aborted once issuing an illegal or impossible write and issuing an illegal read or impossible write, respectively. Reads are meaninglessly performed since the reads are later undone due to the abortion of the transaction in the WA protocol. Reads which can be performed after an illegal read are not performed, i.e. Lost since a transaction is aborted just once issuing an illegal read in the RWA protocol. In the FRWA protocol, a transaction is aborted with some probability once illegally reading an object in order to reduce the number of meaningless and lost reads. We newly introduce the sensitivity concept of an object in order to decide on the abortion probability. The more number of transactions are aborted after illegally reading an object, the more highly sensitive the object is. A transaction which illegally reads a more sensitive object is aborted with higher probability. In the evaluation, we show the execution time of each transaction in the FRWA protocol is shorter than WA and more number of reads can be performed than RWA.