[GitHub] [hbase] ndimiduk commented on a diff in pull request #4954: HBASE-27563 ChaosMonkey sometimes generates invalid boundaries for random item selection

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

ndimiduk commented on code in PR #4954:
URL: https://github.com/apache/hbase/pull/4954#discussion_r1067031749


##########
hbase-it/src/test/java/org/apache/hadoop/hbase/chaos/monkies/PolicyBasedChaosMonkey.java:
##########
@@ -116,13 +116,13 @@ public static <T> T selectWeightedRandomItem(List<Pair<T, Integer>> items) {
 
   /** Selects and returns ceil(ratio * items.length) random items from the given array */
   public static <T> List<T> selectRandomItems(T[] items, float ratio) {
-    int selectedNumber = (int) Math.ceil(items.length * ratio);
-
-    List<T> originalItems = Arrays.asList(items);
+    final int selectedNumber = (int) Math.ceil(items.length * ratio);
+    final List<T> originalItems = Arrays.asList(items);
     Collections.shuffle(originalItems);
-
-    int startIndex = ThreadLocalRandom.current().nextInt(items.length - selectedNumber);
-    return originalItems.subList(startIndex, startIndex + selectedNumber);
+    final int startIndex =

Review Comment:
   Yes, it seems so... and it looks like this patch is not sufficient. Here's the stack trace from branch-2.5.
   
   ```
   2023-01-10T19:33:35,651 WARN  [ChaosMonkey-0] policies.Policy: Exception occurred during performing action: java.lang.IllegalArgumentException: bound must be positive
           at java.base/java.util.Random.nextInt(Random.java:322)
           at java.base/java.util.concurrent.ThreadLocalRandom.nextInt(ThreadLocalRandom.java:449)
           at org.apache.hadoop.hbase.chaos.monkies.PolicyBasedChaosMonkey.selectRandomItems(PolicyBasedChaosMonkey.java:123)
           at org.apache.hadoop.hbase.chaos.actions.RollingBatchRestartRsAction.selectServers(RollingBatchRestartRsAction.java:130)
           at org.apache.hadoop.hbase.chaos.actions.RollingBatchRestartRsAction.perform(RollingBatchRestartRsAction.java:75)
           at org.apache.hadoop.hbase.chaos.policies.DoActionsOncePolicy.runOneIteration(DoActionsOncePolicy.java:48)
           at org.apache.hadoop.hbase.chaos.policies.PeriodicPolicy.run(PeriodicPolicy.java:41)
           at org.apache.hadoop.hbase.chaos.policies.CompositeSequentialPolicy.run(CompositeSequentialPolicy.java:42)
           at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
           at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
           at java.base/java.lang.Thread.run(Thread.java:833)
   ```



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