分布式系统复习.doc

分布式系统分类 --分布式计算系统：集群计算系统网格计算系统（硬件，操作系统，网络都不尽相同） --分布式信息系统：事务处理系统企业应用集成 --分布式普适系统 Grid computing Provide users with seamless access to: Storage capacity Processing Network bandwidth Heterogeneous and geographically distributed systems 系统体系结构： 集中式 非集中式 混合模式 远程过程调用（RPC）： 机器A上的进程调用机器B上的进程时，A上的调用进程被挂起，B上被调用的开始执行调用方可以通过使用参数将信息传送给被调用方，然后可以通过传回的结果得到信息。 RPC操作分为客户部分和服务器部分。 命名系统 Naming Problem Given an essentially unstructured name (e.g., an identi?er), how can we locate its associated access point? Simple solutions (broadcasting) Home-based approaches Distributed Hash Tables (structured P2P) Hierarchical location service Flynn’s Taxonomy 费林分类 SISD 单一指令流单一资料流计算机 单一指令流多资料流计算机 多指令流单一资料流计算机 多指令流多资料流计算机 Subclassifying MIMD memory shared memory systems: multiprocessors no shared memory: networks of computers, multicomputers interconnect bus switch delay/bandwidth tightly coupled systems loosely coupled systems Transparency 透明性 (访问access、位置location、迁移migration、重定位relocation、复制replication、并发concurrency、故障failure) Location transparency:users don’t care where resources are Migration transparency:resources move at will Replication transparency:users cannot tell whether there are copies of resources Concurrency transparency:users share resources transparently Parallelism transparency:operations take place in parallel without user’s knowledge Design issues Transparency Reliability Performance Scalability 目标 (可访问、透明性、开放性、可扩展性、可靠性) Centralized model 集中式模型 No networking Traditional time-sharing system Direct connection of user terminals to system One or several CPUs Not easily scalable Limiting factor: number of CPUs in system Contention for same resources Peer to peer model Each machine on network has (mostly) equivalent capabilities No machines are dedicated to serving others E.g., collection of PCs: Access other people’s files Send/receive email (without server) Gnutella-style content sharing SETI@home computation Processor pool model What about idle workstations(co