topic Re: What does sysgen parameter PE1 affect? in Operating System - OpenVMS

What does sysgen parameter PE1 affect?

M C_1 — Thu, 18 Dec 2003 11:38:29 GMT

Hi all,

Does anyone know what sysgen parameter PE1 affects if used? I know that this parameter is primarily a parameter used on clusters. However, I am curious what other sysgen parameters if could affect.

Anyone have experience with this?

Re: What does sysgen parameter PE1 affect?

Martin P.J. Zinser — Thu, 18 Dec 2003 12:33:08 GMT

Well, hp is pretty specific that you should
keep your fingers off ;-)
To quote:

PE1, PE2, PE3, PE4, PE5, PE6 are reserved for Compaq use only.
These parameters are for cluster algorithms and their usages
can change from release to release. Compaq recommends using the
default values for these special parameters.

Re: What does sysgen parameter PE1 affect?

labadie_1 — Thu, 18 Dec 2003 14:20:24 GMT

Hello

It would be interesting to know your Vms version.
If you are at Vms 7.3 or later, you have the great new item in monitor

$ monitor rlock

if you are before Vms 7.3, you should use the program available at
http://h18000.www1.hp.com/support/asktima/operating_systems/009F6DF1-BC7EC4E1-1C02A1.html

[OpenVMS] Example-C How to Monitor

the Dynamic Lock Remastering Activity

extracted from the above article:

------

PE1 is a dymanic parameter and can be used to control movement of lock
trees OFF of a node, not ONTO a node. It can have different values.

* -1 means that remastering lock trees off the node is disabled.

* 0 means that remastering lock trees of any size can move off
this node.

* Any positive value (100 for example) means that remastering lock
trees up to this size can be moved from this node to another node
of the Cluster.

PE1 is an absolute gate, if PE1 is set to -1 (or 1), trees will only
move on a crash or reboot. They will NOT move due to activity, when
only a single node is interested in a lock, or when there is a
HIGHER LOCKDIRWT on another node.

-------------

Have a look to at

Explanation Of Dynamic Lock Re-Mastering And PE1 Parameter
http://www.compaq.com/support/asktima/operating_systems/0096B379-A2137FC0-1C02A1.html

Re: What does sysgen parameter PE1 affect?

John Gillings — Thu, 18 Dec 2003 15:27:35 GMT

Mike,

Some further explanation...

The heart of clustering on OpenVMS is the Distributed Lock Manager (DLM). This is what allows us to share resources across the cluster in a controlled and secure manner.

Control of an individual lock must be in the hands of a single node (lock master). Any other node which wishes to coordinate against that lock must therefore communicate with the lock master. Internode comms traffic can be expensive, so choosing the "right" lock master is critical to performance.

Typically a lock is mastered by the node on which it is first created. However, over time, activity against the lock may move to other nodes. DLM detects this situation and migrates locks to the "most interested" node. This is called lock remastering. The system parameter LOCKDIRWT also affects which node is chosen to master a shared lock.

For individual locks remastering is rarely a problem. However, for large RMS files and databases, locks are structured into potentially complex "trees", which may contain hundreds or even thousands of sublocks. The entire tree must be mastered by a single node.

In some environments and workloads, we have observed lock trees "hunting" for the best host, migrating from node to node. For a large lock tree remastering can take seconds, or sometimes *minutes* during which an application or even a whole cluster would appear to be hung. Note that a significant fraction of a cluster state transition when a node leaves a cluster is remastering the locks that were mastered by the leaving node.

The PE1 system parameter is used to control lock remastering (see Gerard's note and references for details). We only recommend its use if you experience a problem with inappropriate lock remastering. Otherwise, it's best to leave the DLM to redistribute locks according to activity.

Note that as well as "MONITOR RLOCK" in V7.3, the remastering algorithm was modified. In the past, a lock tree was transferred lock by lock. The tree is now packaged up into much larger chunks, with a significant reduction in remastering time. So, if you have a non-zero value of PE1, maybe try setting it to a higher value (to allow larger trees to be remastered) or try 0.

Re: What does sysgen parameter PE1 affect?

M C_1 — Fri, 19 Dec 2003 09:40:38 GMT

Great answers. This explains what I needed to know about PE1. I appreciate it very much.

I have awarded points to each answer.

Mike