[Linux-cluster] CLVM/GFS2 distributed locking

[Stevo Slavić]

Hello Steven,

I guess license covers only 5.4. Anyway I'm just told it's not an option at
the moment to do the upgrade.


About locking used, ActiveMQ uses Java 6 standard API for trying to acquire
file lock, here is javadoc for the method used:

http://docs.oracle.com/javase/6/docs/api/java/nio/channels/FileChannel.html#tryLock%28long,%20long,%20boolean%29

ActiveMQ tries to obtain non-shared (thus exclusive) lock on whole file on
shared file system, with range from 0 to 1, since the file being locked is
empty. As documentation states, tryLock is non-blocking, it executes
immediately. If ActiveMQ fails to obtain a lock it will  loop (pause and
retry acquiring lock again) until lock is obtained. In initial state first
node obtains lock and becomes master, second one fails to obtain lock and
gets into this loop, as expected. Problem is that slave ActiveMQ on cannot
obtain a lock even after first node gets fenced - it reports that the file
on shared storage is still locked. Simple custom java tool that I made
reports the same, that the file is locked.

OpenJDK 1.6 update 20 is being used as Java runtime. I haven't yet found in
openjdk source exact code which tryLock will call on Linux.


Is there non-Java tool that could be used to reliably check if a file (on
gfs2) is (or can be) exclusively locked (regardless of where the process
holding lock is  running, on same or different node where the tool is being
run)?


Regards,
Stevo.



On Tue, Jan 3, 2012 at 10:59 AM, Steven Whitehouse <swhiteho at redhat.com>wrote:

> Hi,
>
> On Fri, 2011-12-30 at 14:39 +0100, Stevo Slavić wrote:
> > Hello RedHat Linux cluster community,
> >
> > I'm in process of configuring shared filesystem storage master/slave
> > Apache ActiveMQ setup. For it to work, it requires reliable
> > distributed locking - master is node that holds exclusive lock on a
> > file on shared filesystem storage.
> >
> How does it do this locking? There are several possible ways this might
> be done, and some will work better than others.
>
> > On RHEL (5.4), using CLVM with GFS2 is one of the options that should
> > work.
> Why are you using RHEL 5.4 and not something more recent? Note that if
> you are a Red Hat customer, then you should contact our support team who
> will be very happy to assist.
>
> > Third party configured the CLVM/GFS2. I'd like to make sure that
> > distributed locking works OK.
> > What are my options for verifying this?
> >
> I think we need to verify which type of locking the application uses
> before we can answer this,
>
> Steve.
>
> > Thanks in advance!
> >
> > Regards,
> > Stevo.
> > --
> > Linux-cluster mailing list
> > Linux-cluster at redhat.com
> > https://www.redhat.com/mailman/listinfo/linux-cluster
>
>
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