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Parallel and Distributed Systems

Parallel and Distributed Systems


Notes

Parallel & Distributed Systems – B.E.(M.U.) – By Anuradha Bhatia


Video Lectures

CONSISTENCY AND REPLICATION

An important issue in distributed systems is the replication of data. Data are generally replicated to enhance reliability or improve performance. Keeping replicas consistent. Informally, this means that when one copy is updated we need to ensure that the other copies are updated as well; otherwise the replicas will no longer be the same. Client-centric consistency models, concentrate on consistency from the perspective of a single client.


DEADLOCKS

A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set. Resource types R1, R2, . . ., Rm, CPU cycles, memory space, I/O devices. Each resource type Ri has Wi instances.


ELECTION ALGORITHM

The coordinator election problem is to choose a process from among a group of processes on different processors in a distributed system to act as the central coordinator. An election algorithm is an algorithm for solving the coordinator election problem.


FIXED POINT MULTIPLICATION AND CANNON MULTIPLICATION

A pipelined multiplier based on the digit products can be designed using digit product generation logic and the digit adders.


LAMPORT ALGORITHM

Intended to improve the safety in the usage of shared resources. The algorithm of Lamport timestamps is a simple algorithm used to determine the order of events in a distributed computer system. Using mutual exclusion. This algorithm is used to provide a partial ordering of events with minimal overhead, and conceptually provide a starting point for the more advanced vector clock method.


RAYMOND TREE ALGORITHM

Sites are arranged in a logical directed tree. Root: token holder. Edges: directed towards root. Every site has a variable holder that points to an immediate neighbour node, on the directed path towards root. (Root’s holder point to itself). The Raymond Tree follows -Requesting the CS, Executing the CS, Releasing the CS


REMOTE METHOD INVOCATION [RMI]

Remote Method Invocation (RMI) Developed in 1980’s.Allows remote method calls. Objects in different programs can communicate. Method calls appear same as those in same program. Based on Remote Procedure Calls (RPC).


REMOTE PROCEDURE CALL [RPC]

A remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in another address space (commonly on another computer on a shared network), which is coded as if it were a normal (local) procedure call, without the programmer explicitly coding the details for the remote interaction. The programmer writes essentially the same code whether the subroutine is local to the executing program, or remote.


SUZUKI KASAMI BROADCAST ALGORITHM

Completely connected network of processes. There is one token in the network. The owner of the token has the permission to enter CS. Token will move from one process to another based on demand.