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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HELIX-681) Participant should not fail state transition on fail to delete / relay message
Date Wed, 21 Mar 2018 19:09:00 GMT

    [ https://issues.apache.org/jira/browse/HELIX-681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16408436#comment-16408436
] 

ASF GitHub Bot commented on HELIX-681:
--------------------------------------

Github user zhan849 commented on a diff in the pull request:

    https://github.com/apache/helix/pull/152#discussion_r176204863
  
    --- Diff: helix-core/src/main/java/org/apache/helix/util/HelixUtil.java ---
    @@ -219,4 +220,22 @@ public static String serializeByComma(List<String> objects)
{
     
         return idealStateMap;
       }
    +
    +  /**
    +   * Remove the given message from ZK using the given accessor. This function will
    +   * not throw exception
    +   * @param accessor HelixDataAccessor
    +   * @param msg message to remove
    +   * @param instanceName name of the instance on which the message sits
    +   * @return true if success else false
    +   */
    +  public static boolean removeMessageFromZK(HelixDataAccessor accessor, Message msg,
    +      String instanceName) {
    +    try {
    +      return accessor.removeProperty(msg.getKey(accessor.keyBuilder(), instanceName));
    +    } catch (Exception e) {
    --- End diff --
    
    it will not. the reason I did a general try-catch here is because I want to keep removeProperty
semantics (only return true/false) here, but we do have leaked exception in underlying implementations
of removeProperty()


> Participant should not fail state transition on fail to delete / relay message
> ------------------------------------------------------------------------------
>
>                 Key: HELIX-681
>                 URL: https://issues.apache.org/jira/browse/HELIX-681
>             Project: Apache Helix
>          Issue Type: Bug
>            Reporter: Hao Zhang
>            Priority: Major
>
> Currently we have a general try-catch block in HelixTask and HelixTaskExecutor, which,
upon any exception thrown from state transition routine, will fail state transition. However
there are at least the following cases in which state transition should be considered as successful:
>  * When we fail to delete message after successfully handled message and updated current
state -> this is because we already completed state transition and current state is consistent
between participant and ZK
>  * When we fail to send out relay message > as relay message provides only best effort
of delivering messages, which has nothing to do with state transition's results. In case of
fail to relay message, controller will resend message which ensures correctness.



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