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| 2 multi instance questions |
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| sebastia |
 Posted: Tue Nov 18, 2014 9:26 am Post subject: 2 multi instance questions |
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Grand Master
Joined: 07 Oct 2004
Posts: 1003
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There are 2 questions customers always ask about multi-instance queue managers.
I would like to ask your opinions and answers on them both.
a) what mechanism is used to determine that qmgr B (that was idle) can take over the NFS as qmgr A is not owning the filesystem anymore ?
b) how long does it take the takeover to finish ?
Lets imagine 2 compute centers quite distant in meters, but with a nice communications link between them, and the NFS in any one of them
Thanks. Sebastian. |
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| mqjeff |
| Posted: Tue Nov 18, 2014 9:32 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
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| Vitor |
| Posted: Tue Nov 18, 2014 9:37 am Post subject: Re: 2 multi instance questions |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| sebastia wrote: |
| a) what mechanism is used to determine that qmgr B (that was idle) can take over the NFS as qmgr A is not owning the filesystem anymore ? |
Failover will occur when the lock held by qmgr A is released other than by qmgr A receiving an endmqm command. See here. How long this takes is a function of how long it takes NFS to realise "file handle go boom".
| sebastia wrote: |
| b) how long does it take the takeover to finish ? |
How long it takes NFS to realise qmgr A is dead and release the lock + how long it takes qmgr B to start + any NFS level magic needed to mount/unmount the file system (possibly zero)
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| sebastia |
| Posted: Tue Nov 18, 2014 10:04 am Post subject: |
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Grand Master
Joined: 07 Oct 2004
Posts: 1003
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"file lock" is used, ok
But the "passive" or "waiting" qmgr is reading CONTINOUSLY this lock ?
Or does it do it every 3 seconds ?
Or is it configurable ?
In HACMP we had a script we could tune to customer's needs.
Not now, I guess.
By the way ... what is a "file lock" ?
I know NFS has such mechanisms to prevent multiple access to same file, but it is an "internal" mechanism. The second (or later) user is just "blocked" on the access.
Maybe this multi-instance uses this mechanism, so all (if more than one) passive qmgrs are kept "waiting", without any timeout, which would be obviously not configurable.
How wrong am I ?
If I am right, there are few more questions coming to my mind I'd like to share with you, mqseries forum coleagues.
a) what is the name of the file on which the lock is implemented ? (if it is just a single file)
b) how does the active qmgr keep it under its ownership ? It opens it for edit ?
Please, il.luminate my mind, as it gets dark here sometimes, and I really dont like the manuals in electronic form ...
There was a speech on providing them in EPUB format, is it possible ?
Thanks for your patience ! Sebastian. |
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| Vitor |
| Posted: Tue Nov 18, 2014 10:15 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| sebastia wrote: |
| By the way ... what is a "file lock" ? |
Exactly what it sounds like.
| sebastia wrote: |
| I know NFS has such mechanisms to prevent multiple access to same file, but it is an "internal" mechanism. The second (or later) user is just "blocked" on the access. |
Yes, that's the one.
| sebastia wrote: |
| Maybe this multi-instance uses this mechanism, so all (if more than one) passive qmgrs are kept "waiting", without any timeout, which would be obviously not configurable. |
Can you have more than one passive (stand by) queue manager? What do you mean by "timeout" in this context, and what would you want to configure? As I said before, how long it takes NFS to declare qmgr A dead is an NFS matter (which may or may not be configurable, I am not now nor have I ever been an NFS specialist)
| sebastia wrote: |
| How wrong am I ? |
Clearly not very - you know a lot of the concepts.
If I am right, there are few more questions coming to my mind I'd like to share with you, mqseries forum coleagues.
| sebastia wrote: |
| a) what is the name of the file on which the lock is implemented ? (if it is just a single file) |
Why would you want to know this? What value does this information have?
| sebastia wrote: |
| b) how does the active qmgr keep it under its ownership ? It opens it for edit ? |
It opens it exclusively with the appropriate NFS faciltity.
| sebastia wrote: |
| I really dont like the manuals in electronic form ... |
And really, really hate trees? 
| sebastia wrote: |
| There was a speech on providing them in EPUB format, is it possible ? |
Ask IBM.
| sebastia wrote: |
In HACMP we had a script we could tune to customer's needs.
Not now, I guess. |
Not even on AIX if you're using multi-instance and not HACMP.
If you want a script to do this, or you have software other than IIB & WMQ to put under HA, or you want a shared IP across the queue managers because the clients are back version, or any of a number of myriad reasons, use Veritas or another HACMP-like product.
Multi-instance is what it is, and does what it does.
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| Vitor |
| Posted: Tue Nov 18, 2014 10:19 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| Vitor wrote: |
| If you want a script to do this, or you have software other than IIB & WMQ to put under HA, or you want a shared IP across the queue managers because the clients are back version, or any of a number of myriad reasons, use Veritas or another HACMP-like product. |
Sarcasm note:
This comment is entirely serious. My site runs WMB/IIB/WMQ on levels that support multi-instance and we use Sun Cluster Services / HACMP / Veritas for at least all of the reasons I list above, also because we need a certain amount of scripting capability for various (non WMB/IIB/WMQ) parts of the stack.
I'm not denegrating multi-instance. If it fits your needs, use it and be happy. If it doesn't, don't.
Thank you.
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| sebastia |
| Posted: Tue Nov 18, 2014 10:55 am Post subject: |
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Grand Master
Joined: 07 Oct 2004
Posts: 1003
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Thanks for your coments, Vitor.
I agree the product is as it is, and we shall take it for that.
Personally I dont line HACMP neither multi-instance, meaning I would not use them (at the beginning) at my installation.
When you say "file lock is what it sounds like", again you supose you're talking to a english native speaker, and it is not always the case 
When it says "multi-instance" it does not refer to "2-instance", does it ?
Multi instance means "N-instance" to me ...
The timeout was refering to the branch where the passive qmgr "reads" the lock, finds it busy and goes to do other things for a while before returning to try to acquire the lock. A "polling" mechanism, instead of the "blocking" used in NFS.
The name of the file is not a bad thing to know. You know teechies know all kinds of strange stuff that is used to impress both a customer as well as a girl. It is good to have an answer just in case a customer asks, isn't it ?
Electronic books - I did express myself wrong. I meant the browser-like access we have to library. I prefer PDFs.
I bet you agree that
>>> ftp://ftp.software.ibm.com/software/integration/wmq/docs/V7.5/PDFs/
looks miserable as professional level library
Cheers. Sebastian. |
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| JosephGramig |
| Posted: Tue Nov 18, 2014 11:23 am Post subject: |
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Grand Master
Joined: 09 Feb 2006
Posts: 1244
Location: Gold Coast of Florida, USA
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In multi-instance terminology, there is an Active Qmgr and a Standby Qmgr that are both running and looking at file locks. The Active Qmgr is the first one to start and the Standby Qmgr is the second one to start but it does not come all the way up until the file locks indicate the Active is no longer active.
In HA terminology, there is a Qmgr running on an Active node with one or more passive nodes where the Qmgr can be restarted by the HA software. |
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| sebastia |
| Posted: Tue Nov 18, 2014 11:27 am Post subject: |
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Grand Master
Joined: 07 Oct 2004
Posts: 1003
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Josep : you mean "multi-instance" in fact means "2-instance" ?
No way to create3 multi-instance qmgrs on same NFS ? |
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| Vitor |
| Posted: Tue Nov 18, 2014 11:29 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| sebastia wrote: |
| Personally I dont line HACMP neither multi-instance, meaning I would not use them (at the beginning) at my installation. |
HACMP's okay, but you may choose your HA software with the same freedom with which you select ice-cream flavours. Including selecting no ice cream at all if that's your preference.
| sebastia wrote: |
| When you say "file lock is what it sounds like", again you supose you're talking to a english native speaker, and it is not always the case |
Point taken, but I think "file lock" as a term describing a lock on a file is fairly clear even to those with limited English language skills. Which is me, according to all my American co-workers.
| sebastia wrote: |
When it says "multi-instance" it does not refer to "2-instance", does it ?
Multi instance means "N-instance" to me ... |
It does refer to 2-instance, i.e. active and standby. The choice of the word "multi" by the IBM marketing people feeds into the earlier comments surrounding English skills.
| sebastia wrote: |
| The timeout was refering to the branch where the passive qmgr "reads" the lock, finds it busy and goes to do other things for a while before returning to try to acquire the lock. A "polling" mechanism, instead of the "blocking" used in NFS. |
The point here is that the passive queue manager isn't doing any other things; it's just waiting to become active. You can't use it (for example) as a "spare" queue manager.
| sebastia wrote: |
| The name of the file is not a bad thing to know. You know teechies know all kinds of strange stuff that is used to impress both a customer as well as a girl. |
This sort of thing does not impress girls. If your experience is different, I'd like detailed instructions, worked examples and pictures. Also some girls I can call as references, along with details of their native language if not English. And any other relevant details. And pictures.
| sebastia wrote: |
| It is good to have an answer just in case a customer asks, isn't it ? |
I always have an answer when the customer asks. It's often not very technical, in many cases includes content along the lines of "it's something you pay me to worry about" and sometime ends with the phrase "and if you try and "improve" it, I'll have to hurt you. I don't want to hurt you, so don't make me hurt you".
| sebastia wrote: |
| Electronic books - I did express myself wrong. I meant the browser-like access we have to library. I prefer PDFs. |
So do I. If we all ask IBM for the same thing, there's more chance of getting it. I seem to remember there was a RFE once asking for this; you could find it and vote for it (or raise your own and post the link here).
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| JosephGramig |
| Posted: Tue Nov 18, 2014 11:35 am Post subject: |
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| PeterPotkay |
| Posted: Tue Nov 18, 2014 11:44 am Post subject: |
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Poobah
Joined: 15 May 2001
Posts: 7722
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His question is a good one. Assume NFS recognizes instantly the primary QM has released the file locks.
How long before the stand by QM knows this? Does NFS proactively push the change in file lock status to the standby QM? Is the stand by QM checking every ? nano seconds if there has been a change in the file lock status?
I and sebastia want to know How do it know?
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Peter Potkay
Keep Calm and MQ On |
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| Vitor |
| Posted: Tue Nov 18, 2014 11:52 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| PeterPotkay wrote: |
| I and sebastia want to know How do it know? |
| Vitor wrote: |
| I am not now nor have I ever been an NFS specialist) |
Accepting that disclaimer, the file lock is leased as laid out in section 8.6.1 here and when the lease expires (because qmgr A has not renewed it) then the previously blocked client (qmgr B) is given the lock by the NFS server and a file handle is returned to the client, completing the OS call requesting file.
What possible values exist for a lease, how exactly one configures one and the implictions (performance & otherwise) of various lease values I leave to people with better NFS skills.
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Honesty is the best policy.
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| sebastia |
| Posted: Tue Nov 18, 2014 11:57 am Post subject: |
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Grand Master
Joined: 07 Oct 2004
Posts: 1003
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reading the NFS v4 specs at
>>> https://www.ietf.org/rfc/rfc3530.txt
it says ...
| Quote: |
1.4.5. File locking
With the NFS version 4 protocol, the support for byte range file
locking is part of the NFS protocol. The file locking support is
structured so that an RPC callback mechanism is not required. This
is a departure from the previous versions of the NFS file locking
protocol, Network Lock Manager (NLM). The state associated with file
locks is maintained at the server under a lease-based model. The
server defines a single lease period for all state held by a NFS
client. If the client does not renew its lease within the defined
period, all state associated with the client's lease may be released
by the server. The client may renew its lease with use of the RENEW
operation or implicitly by use of other operations (primarily READ). |
So standby qmgr gets locked and waits forever.
When active qmgr does not renew its lease ... NFS server does its job.
A bit more clear.
version 7.5 PDFs - yes, theose are the ones I said look ridicule to me, after all those years of good "Administration", "Clustering", etc
I provided a diferent link, but they are the same ...
Cheers ! |
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| mqjeff |
| Posted: Tue Nov 18, 2014 1:15 pm Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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Also, there's nothing particular that actually *prevents* you from running more than one MI standby qmgr.
It's just not recommended and you won't really have any control over which one gets the file lock first (who's got the button?) |
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