[GitHub] [hive] belugabehr commented on a change in pull request #1197: HIVE-23793: Review of QueryInfo Class

[GitBox <gi...@apache.org>]

belugabehr commented on a change in pull request #1197:
URL: https://github.com/apache/hive/pull/1197#discussion_r454391934



##########
File path: ql/src/java/org/apache/hadoop/hive/ql/QueryInfo.java
##########
@@ -17,48 +17,58 @@
  */
 package org.apache.hadoop.hive.ql;
 
+import java.util.concurrent.TimeUnit;
+
 /**
- * The class is synchronized, as WebUI may access information about a running query.
+ * Provide WebUI information about a running query. Class is thread safe so that
+ * multiple browser sessions can access the data simultaneously.
  */
 public class QueryInfo {
 
   private final String userName;
   private final String executionEngine;
-  private final long beginTime;
   private final String operationId;
-  private Long runtime;  // tracks only running portion of the query.
 
-  private Long endTime;
   private String state;
   private QueryDisplay queryDisplay;
 
+  /*
+   * Times are stored internally with nanosecond precision.
+   */
+  private final long beginTime;
+  private long runtime;

Review comment:
       Thanks for the review.
   
   `synchronized` and `volatile` are not interchangeable.  This class doesn't need synchronization because all of its actions are so trivial, there is no issues with them happening concurrently: just assigning or reading a variable will not cause an issue with multiple threads.  The classic `volatile` case is when a thread is spinning, waiting on some variable to change values.  Without `volatile` the thread may cache the value and never stop spinning.  There is no such use case here, it is for informational purposes only.




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