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https://issues.jboss.org/browse/JGRP-2234?page=com.atlassian.jira.plugin....
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Bela Ban commented on JGRP-2234:
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No, I haven't fixed this yet. As per my other comment on a related issue, I'm not
too happy about {{CENTRAL_LOCK}}, as it doesn't handle network partitions (split brain
scenarios) properly...
I've been thinking to replace / complement the backups with a reconciliation protocol
after the coordinator leaves, where the new coord fetches lock information from all lock
holders and builds its lock table from that information. This means it would take a bit
longer to serve lock requests after a coord change, but we wouldn't need to send
requests from the coord to all backups.
OTOH, this doesn't solve the issue of split brain scenarios and the {{Lock}}
abstraction, which is a bad abstraction to take locks away from someone (after a split
heals) and allows for multiple holders of the same lock during the split...
Unlocked locks stay locked forever
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Key: JGRP-2234
URL:
https://issues.jboss.org/browse/JGRP-2234
Project: JGroups
Issue Type: Bug
Reporter: Bram Klein Gunnewiek
Assignee: Bela Ban
Fix For: 4.0.10
Attachments: ClusterSplitLockTest.java, jg_clusterlock_output_testfail.txt
As discussed in the mailing list we have issues where locks from the central lock
protocol stay locked forever when the coordinator of the cluster disconnects. We can
reproduce this with the attached ClusterSplitLockTest.java. Its a race condition and we
need to run the test a lot of times (sometimes > 20) before we encounter a failure.
What we think is happening:
In a three node cluster (node A, B and C where node A is the coordinator) unlock requests
from B and/or C can be missed when node A leaves and B and/or C don't have the new
view installed yet. When, for example, node B takes over coordination it creates the lock
table based on the back-ups. Lets say node C has locked the lock with name
'lockX'. Node C performs an unlock of 'lockX' just after node A
(gracefully) leaves and sends the unlock request to node A since node C doesn't have
the correct view installed yet. Node B has and recreated the lock table where
'lockX' is locked by Node C. Node C doesn't resend the unlock request so
'lockX' gets locked forever.
Attached is the testng test we wrote and the output of a test failure.
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