[jira] [Comment Edited] (FLINK-27848) ZooKeeperLeaderElectionDriver keeps writing leader information, using up zxid

["Matthias Pohl (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-27848?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17683099#comment-17683099 ] 

Matthias Pohl edited comment on FLINK-27848 at 2/1/23 5:09 PM:
---------------------------------------------------------------

I'm reopening this issue to provide forward(?)ports for 1.16 and 1.17.

Refactoring the leader election for FLIP-285/FLINK-26522 is kind of tricky. I'm trying to slice the code changes into meaningful commits (and ideally dedicated PRs) to make the review process easier.

I ran into this issue when refactoring the code and merging classes into one which also required adapting tests. This revealed the inconsistency/bug in the ZooKeeperLeaderElectionDriver implementation. Merging the bugfixes into 1.17 and 1.16 makes the other changes more reasonable/consistent.

More specifically, this bug was revealed in \{{ZooKeeperLeaderElectionTest.testLeaderShouldBeCorrectedWhenOverwritten}} when changing from the deprecated {{NodeCache}} to {{{}CuratorCache{}}}. The new {{CuratorCacheListener}} allows to be more selective on whether we expect a node creation or change which causes a test failure. The previous test implementation worked because we sent the 2nd write operation after writing the leaderinformation which caused a node-change event and, after all, made the test pass.


was (Author: mapohl):
I'm reopening this issue to provide forward(?)ports for 1.16 and 1.17.

Refactoring the leader election for FLIP-285/FLINK-26522 is kind of tricky. I'm trying to slice the code changes into meaningful commits (and ideally dedicated PRs) to make the review process easier.

I ran into this issue when refactoring the code and merging classes into one which also required adapting tests. This revealed the inconsistency/bug in the ZooKeeperLeaderElectionDriver implementation. Merging the bugfixes into 1.17 and 1.16 makes the other changes more reasonable/consistent.

> ZooKeeperLeaderElectionDriver keeps writing leader information, using up zxid
> -----------------------------------------------------------------------------
>
>                 Key: FLINK-27848
>                 URL: https://issues.apache.org/jira/browse/FLINK-27848
>             Project: Flink
>          Issue Type: Bug
>          Components: Runtime / Coordination
>    Affects Versions: 1.15.0, 1.17.0, 1.16.1
>            Reporter: Xintong Song
>            Assignee: Matthias Pohl
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.15.1
>
>
> After a leadership change, the new leader may keeps writing its information (which is identical) to ZK, causing the zxid on ZK quickly used up.
> The problem is that, in {{ZooKeeperLeaderElectionDriver#retrieveLeaderInformationFromZooKeeper}}, {{leaderElectionEventHandler.onLeaderInformationChange(LeaderInformation.empty())}} is called no matter {{childData}} is {{null}} or not. In case of non-null, this will cause the driver keeps re-writing the leader information to ZK.
> The problem was introduced in FLINK-24038, and only affects the legacy {{ZooKeeperHaServices}}. Thus, only 1.15 are affected.



--
This message was sent by Atlassian Jira
(v8.20.10#820010)