Книга: Distributed operating systems

3.6. SUMMARY

3.6. SUMMARY

This chapter is about synchronization in distributed systems. We started out by giving Lamport's algorithm for synchronizing clocks without reference to external time sources, and later saw how useful this algorithm is. We also saw how physical clocks can be used for synchronization when real time is important.

Next we looked at mutual exclusion in distributed systems and studied three algorithms. The centralized algorithm kept all the information at a single site. The distributed algorithm ran the computation at all sites in parallel. The token ring algorithm passed control around the ring. Each has its strengths and weaknesses.

Many distributed algorithms require a coordinator, so we looked at two ways of electing a coordinator, the bully algorithm and another ring algorithm.

Although all of the foregoing are interesting and important, they are all low-level concepts. Transactions are a high-level concept that makes it easier for the programmer to handle mutual exclusion, locking, fault tolerance, and deadlocks in a distributed system. We looked at the transaction model, how transactions are implemented, and three concurrency control schemes: locking, optimistic concurrency control, and timestamps.

Finally, we revisited the problem of deadlocks and saw some algorithms for detecting and preventing them in distributed systems.

Оглавление книги