Synchronizer (algorithm)
A synchronizer, in the context of distributed computing, is a type of algorithm that allows asynchronous distributed systems to simulate synchronous systems. This is crucial because synchronous systems, where operations occur in lock-step, are often easier to reason about and design algorithms for. However, real-world distributed systems are inherently asynchronous; message delays are unpredictable, and processors may have varying speeds. A synchronizer aims to bridge this gap by adding overhead to the asynchronous system, enabling it to behave approximately like a synchronous one.
The primary goal of a synchronizer is to ensure that all processors advance through a series of logical "rounds" in a coordinated fashion, even though they communicate asynchronously. This coordination typically involves exchanging messages to simulate the behavior of a global clock in a synchronous environment.
Different synchronizer algorithms exist, each with different performance characteristics and assumptions about the underlying asynchronous network. Key considerations for evaluating a synchronizer include:
- Overhead: The amount of extra communication and computation required by the synchronizer, compared to the ideal synchronous algorithm. This overhead is often expressed in terms of rounds of communication or the total number of messages sent.
- Latency: The delay introduced by the synchronizer in completing a round.
- Resilience: The ability of the synchronizer to function correctly even in the presence of message loss or processor failures.
- Network Assumptions: The assumptions made about the asynchronous network, such as bounds on message delays (which are usually not known precisely).
The synchronizer is a fundamental concept in designing distributed algorithms, enabling the adaptation of synchronous algorithms to more realistic asynchronous settings. They are particularly relevant in situations where guaranteed progress and coordination are essential despite the challenges of asynchrony.