topic Re: buffer_limit question in Operating System - OpenVMS

buffer_limit question

Dave Gudewicz — Mon, 14 Nov 2005 15:32:14 GMT

From $help run /buffer_limit

/BUFFER_LIMIT=quota

Specifies the maximum amount of memory, in bytes, that the
process can use for buffered I/O operations or for temporary
mailbox creation.

If you do not specify a buffered I/O quota, the default value
established at system generation time is used. The minimum amount required for any process to execute is 1024 bytes.

************

Q: How does one determine the default value established at system generation time?

Dave...

Re: buffer_limit question

Hein van den Heuvel — Mon, 14 Nov 2005 15:54:08 GMT

Hi there Dave!

The documentation for this is basically under SYS$CREPRC in th system serve ref man:

http://h71000.www7.hp.com/doc/82FINAL/4527/4527pro_025.html#index_x_259

You can do MCR SYSGEN SHOW /PQL
look for BYTLM values

hth,
Hein.

Re: buffer_limit question

Dave Gudewicz — Mon, 14 Nov 2005 16:06:48 GMT

Hein,

You can do MCR SYSGEN SHOW /PQL
look for BYTLM values

***********

There are Min and Def values but I can't seem to find Max values, unless its there and I'm not seeing it.

Dave...

Re: buffer_limit question

Hein van den Heuvel — Mon, 14 Nov 2005 16:26:19 GMT

Right, I do not see a max either.
The sysgen data suggest -1 = infinite as the max.

I think that a practical max is MAXBUF * BUFIO?

Hein.

$ perl -e "foreach (`sysgen show/all`) {print if /BYTLM/}"
PQL_DBYTLM 65536 65536 -1 -1 Bytes D
PQL_MBYTLM 256000 1024 -1 -1 Bytes D
$
$ pipe sysgen show/all | search sys$pipe Dynamic,bytlm
Parameter Name Current Default Min. Max. Unit Dynamic
-------------- ------- ------- ------- ------- ---- -------
PQL_DBYTLM 65536 65536 -1 -1 Bytes D
PQL_MBYTLM 256000 1024 -1 -1 Bytes D
$

Re: buffer_limit question

Wim Van den Wyngaert — Tue, 15 Nov 2005 02:31:03 GMT

You might run out of non-paged dyn memory.

On my system : MAXBUF 64000, BIOLM 12288, so if 12288 buffered IO's are done with big buffers of 64000 bytes, I need about 78MB of non-paged dynamic memory, which I don't have configured (max is 7&MB but 20 is already used).

fwiw

Wim

Re: buffer_limit question

Dave Gudewicz — Tue, 15 Nov 2005 10:04:36 GMT

Wim,

Thanks for the heads up on non-paged dyn.

And I noticed that Hein placed a question mark after MAXBUF * BUFIO = equation.

Dave...

Re: buffer_limit question

Jan van den Ende — Tue, 15 Nov 2005 12:31:24 GMT

Dave,

from your Forum Profile:

I have assigned points to 49 of 104 responses to my questions.

Most of the unassigned threds are quite old.

Maybe you can find some time to do some backlog assigning?

http://forums1.itrc.hp.com/service/forums/helptips.do?#33

Mind, I do NOT say you necessarily need to give lots of points. It is fully up to _YOU_ to decide how many. If you consider an answer is not deserving any points, you can also assign 0 ( = zero ) points, and then that answer will no longer be counted as unassigned.
Consider, that every poster took at least the trouble of posting for you!

To easily find your streams with unassigned points, click your own name somewhere.
This will bring up your profile.
Near the bottom of that page, under the caption â My Question(s)â you will find â questions or topics with unassigned points â Clicking that will give all, and only, your questions that still have unassigned postings.

Closed streams can be re-opened, assigned, and closed again.

Thanks on behalf of your Forum colleagues.

PS. â nothing personal in this. I try to post it to everyone with this kind of assignment ratio in this forum. If you have received a posting like this before â please do not take offence â none is intended!

Proost.

Have one on me.

jpe

Re: buffer_limit question

John Gillings — Wed, 16 Nov 2005 19:05:28 GMT

Dave,

Remember that quotas are really only to protect against accidental or malicious consumption of resources. For trusted, stable, debugged code, you should be able to set them as high as you like.

BYTLM depletion can hang processes in weird states like MUTEX, so it's fairly important to make sure processes have sufficient. You may want to set a quota to a very high value then track a process over time to get some idea of the peak requirement.

Beware of excessively high values for DEFMBXBUFQUO - this may lead to greater than expected consumption of BYTLM.