Shay Shimony created CURATOR-498:
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Summary: LeaderLatch deletes leader and leaves it hung beside a
second leader
Key: CURATOR-498
URL: https://issues.apache.org/jira/browse/CURATOR-498
Project: Apache Curator
Issue Type: Bug
Affects Versions: 4.1.0, 4.0.1
Environment: ZooKeeper 3.4.13, Curator 4.1.0 (selecting explicitly
3.4.13), Linux
Reporter: Shay Shimony
Assignee: Jordan Zimmerman
Attachments: HaWatcher.log, LeaderLatch0.java
The Curator app I am working on uses the LeaderLatch to select a leader out of
6 clients.
While testing my app, I noticed that when I make ZK lose it quorum for a while
and then restore it, then after my app restores it's connection to ZK -
sometimes not all the 6 clients are found in the latch path (using zkCli.sh).
That is, I have 5 instead of 6.
After investigating a little, I have a suspicion that LeaderLatch deleted the
leader in method setNode.
To investigate it I copied the LeaderLatch code and added some log messages,
and from them it seems like very old create() background callback was
surprisingly scheduled and corrupted the current leader with its stale path
name. Meaning, this old one called setNode with its stale name, while sets
itself instead of the leader and deletes the leader. This leaves client
running, thinking it is the leader, while another leader is selected.
If my analysis is correct then it seems like we need to make this obsolete
create callback cancelled.
Please see attached log file and modified LeaderLatch0.
In the log, note that 0000000485 is replaced by 0000000480 and then probably
deleted.
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