[MAPREDUCE-7266] historyContext doesn't need to be a class attribute inside JobHistoryServer

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.3.0, 3.2.2
• Component/s: jobhistoryserver
• Hadoop Flags: Reviewed
• Assignee: Siddharth Ahuja
• Reporter: Siddharth Ahuja
• Created: 08/Jan/20 09:19
• Updated: 21/Mar/22 14:43
• Resolved: 09/Apr/20 10:42

Description

"historyContext" class attribute at https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs/src/main/java/org/apache/hadoop/mapreduce/v2/hs/JobHistoryServer.java#L67 is assigned a cast of another class attribute - "jobHistoryService" - https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs/src/main/java/org/apache/hadoop/mapreduce/v2/hs/JobHistoryServer.java#L131, however it does not need to be stored separately because it is only ever used once in the class, and that too as an argument while instantiating the HistoryClientService class at https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs/src/main/java/org/apache/hadoop/mapreduce/v2/hs/JobHistoryServer.java#L155.

Therefore, we could just delete the lines at https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs/src/main/java/org/apache/hadoop/mapreduce/v2/hs/JobHistoryServer.java#L67 and https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-hs/src/main/java/org/apache/hadoop/mapreduce/v2/hs/JobHistoryServer.java#L131 completely and instantiate the HistoryClientService as follows:

  @VisibleForTesting
  protected HistoryClientService createHistoryClientService() {
    return new HistoryClientService((HistoryContext)jobHistoryService, 
        this.jhsDTSecretManager);
  }