八：The YARN Timeline Server

1、Overview 介紹

    yarn timeline server用於存儲和檢查應用程序過去和如今的信息(好比job history server)。有兩個功能：

1.Persisting Application Specific Information 保存應用程序特定的信息

    收集和檢索應用程序或者框架的特定信息。如裝mr任務的map\reduce數量經過TimeClient發佈到Timeline Server中。而後用戶能夠經過wetrest 來查詢這些參數。

2.Persisting Generic Information about Completed Applications 存儲已經執行完成的應用程序的通用信息

    mr任務有jobhistoryServer來保存歷史任務信息，可是jobhistoryServer只是yarn TimeLine server其中的一個應用。通用信息包括：

• queue-name,   隊列名
• user information and the like set in the ApplicationSubmissionContext,  用戶信息和applicationSubmissonContext的設置
• a list of application-attempts that ran for an application   一系列應用程序而非一個應用
• information about each application-attempt   每一個應用程序的信息
• the list of containers run under each application-attempt 每一個應用程序使用的container列表 
• information about each container. 每一個container的信息
  
  來源： http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/TimelineServer.html

2、Current Status and Future Plans 當前情況和遠景規劃

Current status  當前情況

1. The core functionality of the timeline server has been completed.  核心功能已經完成
2. It works in both secure and non secure clusters.  能夠工做在安全和非安全模式下
3. The generic history service is built on the timeline store.  測探歷史服務已經在timeline store中完成
4. The history can be stored in memory or in a leveldb database store; the latter ensures the history is preserved over Timeline Server restarts. 歷史信息能夠保存在內存或者數據庫中，即便timeline server重啓選樣可用
5. The ability to install framework specific UIs in YARN is not supported.   框架中的特殊UIs不被支持(語法有問題)
6. Application specific information is only available via RESTful APIs using JSON type content. 應用程序特殊的信息只支持RESTful APIs,格式是JSON
7. The 「Timeline Server v1」 REST API has been declared one of the REST APIs whose compatibility will be maintained in future releases.  timeline server V1 的REST APIS是後向兼容的
8. The single-server implementation of the Timeline Server places a limit on the scalability of the service; it also prevents the service being High-Availability component of the YARN infrastructure.  單節點的timeline server的擴展性問題，並且沒法實現HA。

Future Plans 將來規劃

1. Future releases will introduce a next generation timeline service which is scalable and reliable, 「Timeline Service v2」.  下一代的timeline server裝是可擴展和穩定的
2. The expanded features of this service may not be available to applications using the Timeline Server v1 REST API. That includes extended data structures as well as the ability of the client to failover between Timeline Server instances.   使用timeline server v1 的rest api可能沒法使用擴展特性，包括可擴展的數據結構和clinet failover

3、Timeline Structure

Timeline domain

    域，同namespace一個概念，將不一樣的應用和用戶隔開。域中定義和用戶信息、讀寫相關的ACL信息、時間信息等。每一個域在yarn中都必須有獨立的ID。

entity

    實體能夠是appliction\application attempt的元數據， 及用戶定義的信息等。能夠定義實體主過濾器( Primary filters)

event

    實體中應用程序的事件。

4、配置

    默認是不開啓timeline server的。

具體配置請參考：

http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/TimelineServer.html

 

來自爲知筆記(Wiz)