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Posted to common-dev@hadoop.apache.org by "Todd Lipcon (Created) (JIRA)" <ji...@apache.org> on 2012/03/27 00:24:26 UTC
[jira] [Created] (HADOOP-8217) Edge case split-brain race in
ZK-based auto-failover
Edge case split-brain race in ZK-based auto-failover
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Key: HADOOP-8217
URL: https://issues.apache.org/jira/browse/HADOOP-8217
Project: Hadoop Common
Issue Type: Bug
Components: ha
Affects Versions: 0.24.0
Reporter: Todd Lipcon
Assignee: Todd Lipcon
As discussed in HADOOP-8206, the current design for automatic failover has the following race:
- ZKFC1 gets active lock
- ZKFC1 is about to send transitionToActive() and machine freezes (eg GC pause + swapping)
- ZKFC1 loses its ZK lock, ZKFC2 gets ZK lock
- ZKFC2 calls transitionToStandby on NN1, and transitions NN2 to active
- ZKFC1 wakes up from pause, calls transitionToActive(), now we have a bad situation
This is rare, since it requires ZKFC1 to freeze longer than its ZK session timeout, but worth fixing, since the results can be disastrous.
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