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| ZK99TOE |
 Posted: Wed Sep 04, 2013 11:15 am Post subject: How does queue manager work with archiving off? |
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Newbie
Joined: 04 Sep 2013
Posts: 7
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I need to build a new MQ v7.10 queue manager in an environment that has no HSM, no tapes, and very little "spare" DASD. It was suggested that I turn archiving off - setting the CSQ6LOGP parm OFFLOAD to "NO". I was unable to find a reference describing how the queue manager behaves in this scenario when an active log is full and ready to offload to an archive dataset.
Another suggestion was to create the archive logs but define them as "SHR" so they could be over-written. Obviously we would be using circular logging.
This is a test queue manager exclusively. The testers would run scripts to test transaction processing through the queue manager to remote queue managers, so my understanding is that re-running the process is not an issue.
Any input or ideas welcomed. Thanks! |
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| Vitor |
| Posted: Wed Sep 04, 2013 3:25 pm Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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Moved to Mainframe section
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| Vitor |
| Posted: Wed Sep 04, 2013 3:34 pm Post subject: Re: How does queue manager work with archiving off? |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| ZK99TOE wrote: |
| I was unable to find a reference describing how the queue manager behaves in this scenario when an active log is full and ready to offload to an archive dataset. |
Nothing except a console message. Once all the active logs are full nothing will happen to your queue manager at all until an offload happens. Literally. All the applications will hang and no other WMQ activity will occur.
| ZK99TOE wrote: |
| Another suggestion was to create the archive logs but define them as "SHR" so they could be over-written. |
Who suggested that? Someone who enjoys jumping out of aircraft without a parachute? Even on a test server that's going to break.
| ZK99TOE wrote: |
| Obviously we would be using circular logging. |
So WMQv7.1 on z/OS now supports circular logging? I must have missed that in the new feature for WMQv7.1. If you're using circular logging (which WMQv7.0 and below does not offer on z/OS) why are you worrying about archive logs?
| ZK99TOE wrote: |
| This is a test queue manager exclusively. The testers would run scripts to test transaction processing through the queue manager to remote queue managers, so my understanding is that re-running the process is not an issue. |
But the processes not running at all presumably will be? Why are test messages set up to go through the logs anyway? Why are you retaining archive logs if you don't care (and think using SHR is a good idea)?
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| bruce2359 |
| Posted: Wed Sep 04, 2013 4:12 pm Post subject: Re: How does queue manager work with archiving off? |
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Poobah
Joined: 05 Jan 2008
Posts: 9396
Location: US: west coast, almost. Otherwise, enroute.
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| ZK99TOE wrote: |
| Obviously we would be using circular logging. |
Nope. Circular logging is a midrange-only WMQ option.
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| gbaddeley |
| Posted: Wed Sep 04, 2013 4:39 pm Post subject: Re: How does queue manager work with archiving off? |
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Jedi
Joined: 25 Mar 2003
Posts: 2494
Location: Melbourne, Australia
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| bruce2359 wrote: |
| ZK99TOE wrote: |
| Obviously we would be using circular logging. |
Nope. Circular logging is a midrange-only WMQ option. |
I regard the z/OS MQ logs as circular, in that there is are a fixed number of datasets that are reused in a circular fashion. z/OS has the nice feature of taking an archive copy of older logs. I wish distributed platforms could do that with circular logs.
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| bruce2359 |
| Posted: Wed Sep 04, 2013 8:06 pm Post subject: Re: How does queue manager work with archiving off? |
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Poobah
Joined: 05 Jan 2008
Posts: 9396
Location: US: west coast, almost. Otherwise, enroute.
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| gbaddeley wrote: |
| bruce2359 wrote: |
| ZK99TOE wrote: |
| Obviously we would be using circular logging. |
Nope. Circular logging is a midrange-only WMQ option. |
I regard the z/OS MQ logs as circular, in that there is are a fixed number of datasets that are reused in a circular fashion. z/OS has the nice feature of taking an archive copy of older logs. I wish distributed platforms could do that with circular logs. |
We have a definition problem with regard to 'reused.'
MVS log datasets are not usually reused. Most often, I've seen log datasets be GDGs, with n generations. When the n limit is reached, older generations are migrated, or perhaps deleted; but the dataset (name and extents) are not usually reused in-place.
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| elkinsc |
| Posted: Thu Sep 05, 2013 6:01 am Post subject: Logging in a production z/OS queue manager |
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Centurion
Joined: 29 Dec 2004
Posts: 138
Location: Indy
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The logging mechanism on z/OS is something like circular logging, with the addition of the archive capability. There is a pool of active logs, when one fills it is switched to the next in the list (like circular logs). The one just filled is then archived, sometimes to a GDG, sometimes to tape, based on how archiving is set up. Once the archive is complete the log is flagged as available for reuse.
For production queue managers, archiving should never be turned off. Traditionally, archiving protects the queue manager (and you as an administrator) from possible loss of data. From a practical perspective, as mentioned in another thread; if archiving is off, there is an active UOW on the 'next' log in the pool, and the log needs to switch the queue manager will stop processing persistent messages. That only leads to calls and complaints, something all administrators like to avoid.
Even if the original plans are to use non-persistent messaging exclusively, applications do what they will on setting persistence. |
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| Vitor |
| Posted: Thu Sep 05, 2013 7:09 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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The point, which I think should be stressed for our less experienced readers, is that z/OS does not support circular logging as the concept familiar to people on distribted.
There are any number of ways we more experienced types can fake / spoof / forge / recreate it on z/OS but that's a more advanced discussion.
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| bruce2359 |
| Posted: Thu Sep 05, 2013 7:18 am Post subject: |
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Poobah
Joined: 05 Jan 2008
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Location: US: west coast, almost. Otherwise, enroute.
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Or, more precisely, on WMQ for z/OS there is no circular vs. linear option.
WMQ uses DB2's logging infrastructure. Log segments (datasets) are allocated, initialized, and registered (NEWLOG command) in the BSDS, prior to use.
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| Vitor |
| Posted: Thu Sep 05, 2013 7:35 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
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Location: Texas, USA
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| bruce2359 wrote: |
| Or, more precisely, on WMQ for z/OS there is no circular vs. linear option. |
I accept your increased precision
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| ZK99TOE |
| Posted: Fri Sep 06, 2013 5:53 pm Post subject: How does queue manager work with archiving off? |
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Newbie
Joined: 04 Sep 2013
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I wrote the original post. Apologies for calling what z/OS does with logging as 'circular' - I get your point about accuracy in verbage.
As no one responded to my *real* question of how MQ responds when the log dataset gets full and archiving is turned off (OFFLOAD is set to "NO"), I tested it.
MQ just writes to a log until it is full, and then goes to the next log, and the next, until it runs out of logs and starts over-writing to the first. No archive datasets created, no call for archiving, no stopping of queue managers. No other LOG parms were changed. That was the original question. Perhaps that was not clear. |
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| bruce2359 |
| Posted: Sat Sep 07, 2013 7:29 pm Post subject: |
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Poobah
Joined: 05 Jan 2008
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Location: US: west coast, almost. Otherwise, enroute.
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Repeat your tests (plural and concurrent) with large UofWs.
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Lex Orandi, Lex Credendi, Lex Vivendi. As we Worship, So we Believe, So we Live. |
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| Vitor |
| Posted: Mon Sep 09, 2013 4:37 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| bruce2359 wrote: |
| Repeat your tests (plural and concurrent) with large UofWs. |
And ensure the messages are persistent.
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| Vitor |
| Posted: Mon Sep 09, 2013 4:38 am Post subject: Re: How does queue manager work with archiving off? |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| ZK99TOE wrote: |
| As no one responded to my *real* question of how MQ responds when the log dataset gets full and archiving is turned off (OFFLOAD is set to "NO"), I tested it. |
Yes I did. 
| ZK99TOE wrote: |
| MQ just writes to a log until it is full, and then goes to the next log, and the next, until it runs out of logs and starts over-writing to the first. No archive datasets created, no call for archiving, no stopping of queue managers. No other LOG parms were changed. |
And under exactly what kind of message load?
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| elkinsc |
| Posted: Mon Sep 09, 2013 6:12 am Post subject: The archives and this post |
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Centurion
Joined: 29 Dec 2004
Posts: 138
Location: Indy
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have your question answered, and the question was answered in this post. So to repeat myself and others:
For production queue managers, archiving should never be turned off. Traditionally, archiving protects the queue manager (and you as an administrator) from possible loss of data.
WHEN ARCHIVING IS TURNED OFF:
If the current log is full and the 'next' log in the pool has entries from an active UOW, the queue manager will stop processing persistent messages. You will get messages that indicate the problem. If this happens in production (and it will) you will get calls and complaints. 'MQ is broken!' - the 'again" is silent.
I have seen queue managers run fine for years with archiving turned off (saving DASD), then his a sudden spike or an application problem which causes havoc. Fixing the issue in an emergency is much more costly than doing it right initially. |
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