Re: [jgroups-users] questions about CENTRAL_LOCK locking service under 3.6.11

On 10/10/17 8:42 PM, Questions/problems related to using JGroups wrote:
> Hey folks:
>
> I'm having problems all of a sudden with the CENTRAL_LOCK locking service.  The behavior is that locks seem to timeout even though I have generated an unlock on all boxes on the channel and have also tried rebooting them all in turn.  I am working on a forked channel and other traffic through the channel seems to be working fine.

If you look at the coordinator, does it list all locks?

> I've got this state right now in production with a lot of JMX control to take a look at telemetry.  I see asymmetric print-locks output from CENTRAL_LOCK on the nodes in the channel.  I see consistent views.  I'm going to try to drop to 1 FE for a short time this evening to see if I can get this to clear.

What do you mean by asymmetric output? The printout at the coord and the 
backup (next in line) should be the same, all others (unless you changed 
num_backups) should *not* have any (server) locks.

>
> - Anything else I can do to debug this issue?

CENTRAL_LOCK and its superclass Locking have operations 
(@ManagedOperation) that can be invoked to dump all locks and their 
owners. e.g. 'probe.sh op=CENTRAL_LOCK.printLocks' will dump all locks 
and their owners. Check that for consistency.

Note that the lock service in JGroups _can_ lead to multiple owners 
holding the same lock at the same time in case of a split brain. You'd 
have to resort to jgroups-raft to enforce at-most-once semantics.

> - I can't find the change-log for jgroups so I don't know if 3.6.12-14 have fixed problem there

Take a look at [1] and go from 3.6.12 to 3.6.14


[1] 
https://issues.jboss.org/projects/JGRP?selectedItem=com.atlassian.jira.jira-projects-plugin:release-page&status=released

>
> Thanks,
> gray
>
>
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-- 
Bela Ban, JGroups lead (http://www.jgroups.org)


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