GrantPSpencer opened a new pull request, #2886:
URL: https://github.com/apache/helix/pull/2886

   ### Issues
   
   - [ ] My PR addresses the following Helix issues and references them in the 
PR description:
   
   #2885 
   Helix stoppable does not account for multiple replicas in the same fault 
zone. This can occur during instance operations such as swap but also as a 
result of the issue linked above. 
   
   ### Description
   
   - [ ] Here are some details about my PR, including screenshots of any UI 
changes:
   
   Currently, the batch stoppable check parallelizes the 
performHelixOwnInstanceCheck, which includes the min active replica check. This 
parallelization works on the assumption that a single partition will not have 
more than 2 replicas hosted in 1 fault zone. This assumption is not fully 
correct as n+1 transitions can result in 2 replicas in the same fault zone, as 
well instance operations such as SWAP. 
   
   The parallelization of the other helix health checks can be kept to not lose 
out on that optimization. The min active check can then be done sequentially 
for each instance. 
   
   There is a potential for optimizing the min active replica check. Currently 
it is done per instance and reads the externalView and idealStates for each 
resource from ZK. It could be optimized to read the EVs and IS's once and use 
those for all instances the check is being ran on. However, I did not want to 
complicate this first draft of the PR with that refactoring. 
   
   
   ### Tests
   
   - [ ] The following tests are written for this issue:
   
   TestInstancesAccessor.java#testMultipleReplicasInSameMZ
   
   - The following is the result of the "mvn test" command on the appropriate 
module:
   
   ```
   $ mvn test -o 
-Dtest=TestPerInstanceAccessor,TestInstancesAccessor,TestMaintenanceManagementService
 -pl=helix-rest
   
   [INFO] Results:
   [INFO] 
   [INFO] Tests run: 45, Failures: 0, Errors: 0, Skipped: 0
   [INFO] 
------------------------------------------------------------------------
   [INFO] BUILD SUCCESS
   [INFO] 
------------------------------------------------------------------------
   [INFO] Total time:  02:31 min
   [INFO] Finished at: 2024-08-15T20:43:09-07:00
   [INFO] 
------------------------------------------------------------------------
   
   ```
   
   ### Changes that Break Backward Compatibility (Optional)
   
   - My PR contains changes that break backward compatibility or previous 
assumptions for certain methods or API. They include:
   
   Not a significant incompatibility, but the STOPPABLE_CHECK_LIST no longer 
contains the min_active_replica check as it is done separately. 
   
   ### Commits
   
   - My commits all reference appropriate Apache Helix GitHub issues in their 
subject lines. In addition, my commits follow the guidelines from "[How to 
write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Code Quality
   
   - My diff has been formatted using helix-style.xml 
   (helix-style-intellij.xml if IntelliJ IDE is used)
   


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