Distributed lock manager: Difference between revisions

Revision as of 01:12, 24 March 2006

Revision as of 14:57, 24 March 2006

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A '''distributed lock manager''' (DLM) provides distributed applications with a means to synchronize their accesses to shared resources.

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==Clusters==

Each machine in a [[VMScluster]] runs a separate instance of the [[OpenVMS]] [[operating system]], but sees a unified view of all the disks attached to the cluster, with cluster-wide [[file locking]]. This is accomplished by using a DLM to not only manage the locks but also coordinate all disk access.

Combining two or more computers into a [[computer cluster|cluster]] in which the machines can use each other's hard disks via a unified file system offers significant advantages for performance and [[high-availability|availability]]. DLMs have been used as the foundation for clustered file systems with considerable success by using cluster wide locks not only for [[file locking]] but also for coordination of all disk access. [[VMScluster]], the first clustering system to come into widespread use, relied on the [[OpenVMS]] DLM in just this way.

[[Red Hat]] and [[Oracle Corporation|Oracle]] have both developed clustering software for [[Linux]]. Both projects include a DLM modelled on the venerable [[OpenVMS|VMS]] DLM. (''OCFS2'', the Oracle Cluster File System[http://oss.oracle.com/projects/ocfs2/] has been included[http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=29552b1462799afbe02af035b243e97579d63350] in version 2.6.16 of the official [[Linux kernel]]. Red Hat's cluster software[http://sources.redhat.com/cluster/], including their DLM[http://sources.redhat.com/cluster/dlm/] is available as a kernel patch.)

==SSI Systems==

A DLM is also a key component of more ambitious [[Single-system image|single system image]] projects such as [[OpenSSI]].