7 Distributed System notes：A feature of distributed system - Transparency (分布式系統的透明性特征)

以前對分布式系統透明性特征的了解比較模糊，甚至相左。現在來重新了解、陳述地總結一下。首先，我們對透明性做一個通俗的解釋。透明性是把事物複雜的細節和特點進行隐藏，也可以簡單地了解為通過抽象化或封裝的手段對使用者和開發人員隐蔽系統或服務的複雜性等，而并非是把細節暴露的意思。

下面我們列出ANSA參考手冊和國際标準化組織定義的八種開放分布式處理參考模型的透明性。

• Access transparency enables local and remote resources to be accessed using

  identical operations.

  通路透明性：用相同的操作通路本地資源和遠端資源。

• Location transparency enables resources to be accessed without knowledge of their physical or network location (for example, which building or IP address).

  位置透明性：不需要知道資源的實體或網絡位置（例如，哪個建築物或IP位址）就能夠通路它們。

• Concurrency transparency enables several processes to operate concurrently using

  shared resources without interference between them.

  并發透明性：幾個程序能并發地使用共享資源進行操作且互不幹擾。

• Replication transparency enables multiple instances of resources to be used to

  increase reliability and performance without knowledge of the replicas by users or

  application programmers.

  使用資源的多個執行個體提升可靠性和性能，而使用者和應用程式員無須知道副本的相關資訊。

• Failure transparency enables the concealment of faults, allowing users and

  application programs to complete their tasks despite the failure of hardware or

  software components.

  故障透明性：屏蔽錯誤，不論是硬體元件故障還是軟體故障，使用者和程式員都能過完成他們的任務。

• Mobility transparency allows the movement of resources and clients within a system

  without affecting the operation of users or programs.

  移動透明性：資源和客戶能夠在系統内移動而不會影響使用者或程式的操作。

• Performance transparency allows the system to be reconfigured to improve

  performance as loads vary.

  性能透明性：當負載變化時，系統能重新配置以提高性能。

• Scaling transparency allows the system and applications to expand in scale without change to the system structure or the application algorithms.

  伸縮透明性：系統和應用能夠進行拓展而不改變系統結構或應用算法。

The two most important transparencies are access and location transparency; their presence or absence most strongly affects the utilization of distributed resources. They are sometimes referred to together as network transparency.

References

分布式系統：概念與設計 第五版