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| anderc1 |
 Posted: Fri Apr 25, 2008 7:46 am Post subject: MQChl MaxMsgL & memory usage. |
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Acolyte
Joined: 11 Sep 2002
Posts: 55
Location: Research Triangle Park, NC
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Just read something in an internal doc that first made me grin, then it made me curious. It said the larger the message the more memory required by the channel. This is something I've never thought about or can recall reading about.
Is there any correlation between the Max Message Length setting on a sender channel and the amount of memory used by that channel at startup?
The channel is going to xmit in what 32K chunks regardless of message size?
So what would the actual memory usage for a channel be? |
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| bruce2359 |
| Posted: Fri Apr 25, 2008 7:50 am Post subject: |
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Poobah
Joined: 05 Jan 2008
Posts: 9469
Location: US: west coast, almost. Otherwise, enroute.
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| Just read something in an internal doc... |
What internal doc? Please post a url to it, or quote the relevant sections.
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| jefflowrey |
| Posted: Fri Apr 25, 2008 7:54 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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And, of course, you're not discussing IBM confidential material on a public forum?
Also, I believe the answers to your question are "no", "yes-ish", and "based on need".
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I am *not* the model of the modern major general. |
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| anderc1 |
| Posted: Fri Apr 25, 2008 9:51 am Post subject: |
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Acolyte
Joined: 11 Sep 2002
Posts: 55
Location: Research Triangle Park, NC
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Sorry, should have clarified. Internal = My employer internal and no not IBM. Sorry can't share it, need the paycheck.
It was just one of those things you see from time to time where you get someones else's understanding of how things in MQ work versus your understanding. I hate to call someone wrong or correct them without confirming. Now Jeff, if you happen to know of an IBM doc that goes into the details of the MCA and how it works, do feel free to share.  |
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| jefflowrey |
| Posted: Fri Apr 25, 2008 10:09 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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As far as I know, and I don't know that this is discussed externally at all, the MCA is going to allocate memory for messages "as needed", and not for example allocate a message buffer of 100MB "just in case".
And I don't know what's going to go on with TCP/IP packet size or message chunk size as data flows over the channel.
There's likely some information on both of these buried in the Intercommunications manual.
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I am *not* the model of the modern major general. |
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| PeterPotkay |
| Posted: Fri Apr 25, 2008 10:16 am Post subject: |
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Poobah
Joined: 15 May 2001
Posts: 7722
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Also take a look at the Performance Support packs which allude to the fact that the bigger messages, the more memory a channel uses.
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Peter Potkay
Keep Calm and MQ On |
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| bruce2359 |
| Posted: Fri Apr 25, 2008 10:20 am Post subject: |
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Poobah
Joined: 05 Jan 2008
Posts: 9469
Location: US: west coast, almost. Otherwise, enroute.
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| My employer internal ... |
Be cautious about this type of documentation. It might be old, might refer to v5 or v2 - who knows. In any case, at least ask when it was written, and when it was last updated - if ever.
Stuff like this leads to IROTs - Irrational Rules of Thumb, from which you make irrational decisions about hardware, o/s settings, application design, and so on.
I applaud your curiousity; but please temper it with the absolute realization that whatever and however something is done today, history has proven that it will likely change out from under your in-house doc - along with other mythical beliefs.
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I like deadlines. I like to wave as they pass by.
ב''ה
Lex Orandi, Lex Credendi, Lex Vivendi. As we Worship, So we Believe, So we Live. |
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| anderc1 |
| Posted: Mon Apr 28, 2008 6:55 am Post subject: |
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Acolyte
Joined: 11 Sep 2002
Posts: 55
Location: Research Triangle Park, NC
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This is going to drive me crazy until I figure it out, so I'm going to go dig through the Intercommunications Manual and performance reports as suggested. This is one of those issues I'd like to pin one of the Hursley guys down and pick his brain. Maybe we need a Ask Hursley forum so when the conference comes around, we have all the "undocumented" questions/issues in one place and the people with the answers in one place.
Thanks guys,
If I find anything earth shattering I'll post it. |
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| Vitor |
| Posted: Mon Apr 28, 2008 7:05 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| anderc1 wrote: |
| This is one of those issues I'd like to pin one of the Hursley guys down and pick his brain. |
I'm forced to ask "what issue?" Are you getting memory probems? Throughput problems? Or is it simply this internal document predicting fire and destruction with large messages? IMHO if it's all working put this document back where you found it and walk away. 
| anderc1 wrote: |
Maybe we need a Ask Hursley forum so when the conference comes around, we have all the "undocumented" questions/issues in one place and the people with the answers in one place.
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This stuff tends to be undocumented for a reason, and one of the reasons is it changes from release to release! Even if you got the answer (and it's a big assumption that there's only one answer) it's probably not wise to rely on it.
Other opinions welcomed, especially from those blessed ones who would be on the sharp end of such a forum.....?
Short term, try the Hursley blog & see if any one has information from you there.
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Honesty is the best policy.
Insanity is the best defence. |
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| anderc1 |
| Posted: Mon Apr 28, 2008 9:39 am Post subject: |
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Acolyte
Joined: 11 Sep 2002
Posts: 55
Location: Research Triangle Park, NC
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| No issues, it's just when I read the doc, my first thought was B.S., as I had not read or heard of any affect on MQ or the system by setting the maxmsglgth attribute of a channel higher than the 4mb default. I suspect, someone may have taken a liberty, based on the affect of large messages on system resources, essentially creating a fear factor for those that may have limited experience with MQ. I think most of us look at the MCA and conclude that it works, because it does, not specifically how it works. A doc or discussion specific to the MCA would be nice and may exist, just haven't found it yet. |
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| PeterPotkay |
| Posted: Mon Apr 28, 2008 10:05 am Post subject: |
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Poobah
Joined: 15 May 2001
Posts: 7722
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| anderc1 wrote: |
| No issues, it's just when I read the doc, my first thought was B.S., as I had not read or heard of any affect on MQ or the system by setting the maxmsglgth attribute of a channel higher than the 4mb default. |
If THATs what your doc says then you're right, its wrong. Once a channel starts up it will use more memory the bigger the messages are. But you can define 500 channels all with 100MB as their Max Message Size and that will have ZERO effect on the QM if the channel defs are just sitting there unused.
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Peter Potkay
Keep Calm and MQ On |
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| anderc1 |
| Posted: Mon Apr 28, 2008 10:32 am Post subject: |
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Acolyte
Joined: 11 Sep 2002
Posts: 55
Location: Research Triangle Park, NC
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Thanks Peter! That was my understanding and what Jeff said as well, so unless someone at Hursley calls B.S. on us, that's what I'm going with. Now I'll have to go find another problem to conquer.  |
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| bruce2359 |
| Posted: Mon Apr 28, 2008 12:43 pm Post subject: |
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Poobah
Joined: 05 Jan 2008
Posts: 9469
Location: US: west coast, almost. Otherwise, enroute.
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What you have stumbled on is the difference between: "how does it work," and "exactly how does it work." The manuals address "how does it work."
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I like deadlines. I like to wave as they pass by.
ב''ה
Lex Orandi, Lex Credendi, Lex Vivendi. As we Worship, So we Believe, So we Live. |
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