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vms problems

 
tim lloyd_1
Frequent Advisor

vms problems

I maintain a legacy system which relies on qios to communicate with the outside world. The system runs on HP Itanium under VMS8.2. The language is pascal and makes heavy use of shared memory.

Action is initiated by logging in as a specific VMS user, the login command file associated with this user runs through some setup commands and then starts a number of detached processes. Each process has its quotas throttled at this point.

This is a transaction processing system which receives requests via ethernet from a number of external processing devices. The messages are processed sequentially and responses sent back to the originator via the same processing device.

There are also a number of unsolicited messages send out from Itanium to the processing devices. Ultimately, we are looking at fielding and responding to approx 100 requests/second.

The system has been in place since 1992 with minimal problems. Recently we added more processing devices to the setup, hence more load.

We have been experiencing problems when issuing qio's – process quota exceeded. This system is running at a customer's site so I can not monitor which quota was being exceeded. I increased the AST limit for the process experiencing problems. This has caused the error to shift and I now get an error on a call to lib$remqhi. Unfortunately the code does not highlight the exact error, simply crashes the program from a non-recoverable error. The program is restarted and does not experience the problem again during the trading day.

So, it looks like raising the AST limit addressed one problem but it looks like a number of other quotas should be increased in line with this change. A suggestion I received was to upgrade BIOLM, DIOLM and BYTLM.

I guess where I am coming from here is: does the explanation above make any sense? If so, can anyone comment on the quotas I have raised and those I would like to raise? Are there any other quotas which should rise in line with those mentioned? Unfortunately I have inherited a system which seems to have architectural problems and my experience of VMS is limited in this field.
12 REPLIES 12
Steven Schweda
Honored Contributor

Re: vms problems

I know nothing, but ...

> [...] can anyone comment on the quotas [...]

You could. I don't know what they were. I
don't know what they are. Actual values
might be interesting. Something could be
absurdly low, but my psychic powers are too
weak to let me discover anything from here.

If you're worried about the process quotas,
why not just try raising them? What could go
wrong? I might point a shotgun toward the
whole mess, and see if a factor of two
helped. If so, then a curious person could
try a set of more controlled increases to
see what actually mattered. If not, look
elsewhere.

Some basic SHOW PROCESS /QUOTA commands
scattered throughout a typical day might
reveal a pattern as something or other
shrinks toward zero.
tim lloyd_1
Frequent Advisor

Re: vms problems

Hi Steven, point taken about the lack of info. I have been monitoring the situation today and no problems at all. The quotas have remained constant over a 4 hr sample. the attachment has the last figures I recorded.

I have previously changed ASTs from 100 to 300 and I am planning to do the same with Buffered I/O limit and Direct I/O limit. Does that make sense? How do the other quotas look? TIA
Jan van den Ende
Honored Contributor

Re: vms problems

Tim,

to begin with:
WELCOME to the VMS forum!

Secondly:
Please rename any attachment to the extension .txt before posting. That way they should be more acceptable to most browsers.

Steven's suggestion about doubling is very reasonable. Without info on the exact quotum it is a hard guess otherwise.
You might do a SET PROCES/DUMP in the routine that kicks off the process, and the then generated dump MIGHT reveal more precise info (unless the programm explicitly obscures it, which, alas, is non too uncommon).

Bext to BIOLM and DIOLM you might also raise ENQLM at those transaction numbers. In todays memory-rich systems the impact on resource use is VERY minor.
For BYTLM I would start at 4-fould (or maybe 10-fold)

Happy hunting!

Proost.

Have one on me.

jpe
Don't rust yours pelled jacker to fine doll missed aches.
Robert Gezelter
Honored Contributor

Re: vms problems

Tim

Welcome to the OpenVMS forum!

Raising the quotas is one stop-gap. If the problem is a short-term burst of activity, this may resolve the problem entirely.

However, it might be more productive in the long term to do also enable and then analyze process dumps to actually understand what is happening. This would also allow guidance to be developed as to future increases in resource requirements as workload further increases. I may have some gray hair, but I would rather increase quotas based upon a formula based on workload than just keep increasing it (e.g., I do get worried when I need to add oil to the car between scheduled changes; the same with coolant -- if fluids are disappearing, they must be going somewhere, at best there is a loose connection, at worst it is something serious, possibly fatal).

Applications of the general class described in the OP often have resource requirements denominated in circuits and transactions. A surge in resource usage beyond that formula often indicates something amiss.

Applications using shared memory are also very demanding of correctness. Higher performance systems often change the timing and uncover latent problems. Are there any other anomalies besides quotas being exceeded?

- Bob Gezelter, http://www.rlgsc.com
tim lloyd_1
Frequent Advisor

Re: vms problems

Hi Folks, thanks for the responses so far. I appreciate the thoughts. I have tried to dump the contents of the sh proc/quota, the presentation is not the best but I think the salient details are there.

If you have any comments based on the below I would be grateful. I have to duck out for the night.

Noted about tuning the solution. First step is to get the customer off my back so I can work without people breathing down my neck :)

Process Quotas:

CPU limit: Infinite Direct I/O limit: 100
Buffered I/O byte count quota: 535648 Buffered I/O limit: 100
Timer queue entry quota: 472 Open file quota: 1167
Paging file quota: 2242800 Subprocess quota: 13
Default page fault cluster: 64 AST quota: 299
Enqueue quota: 3997 Shared file limit: 0
Max detached processes: 0 Max active jobs: 0