what is a distributed system。 Lamport is defined as: "If you have never heard of a computer crash causing you to do nothing, it means that you are dealing with a distributed system." A more general definition is that a distributed system is a combination of several independent computers that, for the user, are like a single related system.
the most distributed featuresis to hide the internal organizational structure of the system from the user, and the differences between the various computers and the way the communication between computers are hidden. Users can interact with distributed systems in a consistent and unified manner, whenever and wherever they are. A truly value-for-money distributed system with
four key goals: 1, make resources accessible, this is the most important goal of distributed system, 2, transparency. As you can see from the definition, a distributed system needs to hide the fact that its processes and resources are actually distributed across multiple computers. There are many kinds of transparency: 2.a, access transparency: the different data representation and the hiding of the way of accessing resources; 2.b, location transparency: Users cannot discriminate the physical location of resources in the system, which is achieved by naming; 2.c, migration transparency: resource movement does not affect how the resource is accessed; 2.d , reposition transparency: resources are relocated while receiving access, without the user and application's attention; 2.e, replication transparency: the fact that there are multiple copies of the same resource is hidden; 2.f, concurrency transparency: When accessing shared resources, Let no one user feel that others are also using the resources they are using; 2.g, failure transparency: the user will not notice that a resource is not working properly and the system then recovers from the failure. 3, openness. Distributed systems provide services based on a set of guidelines that describe the syntax and semantics of the services provided, summarize these rules, formalize them, and form a protocol; 4. Scalability. This includes scale expansion, geographic expansion, and the scalability of management. There are many kinds of organizational structure of distributed systems, and one important type is that machines are divided into customers and servers. Customer-server architectures are often highly centralized, and in a decentralized architecture, the processes that make up the distributed system play the same role, which is a point-to-point system. Distributed system needs to focus on the following aspects trade-off, around the key objectives of the distributed system design, in solving the problem of distributed system design, always keep the focus on the goal is beneficial: 1, Process 2, communication 3, naming 4, synchronization 5, consistency and replication 6, fault tolerance 7, security
Initial knowledge of distributed systems
