topic Re: How do I increase free list size in Operating System - OpenVMS

How do I increase free list size

Paul cotton — Wed, 12 Mar 2008 07:53:07 GMT

Could someone please tell me what i need to do in order to increase the free list size on an AlphaServer.

Re: How do I increase free list size

Karl Rohwedder — Wed, 12 Mar 2008 08:11:36 GMT

Re: How do I increase free list size

Jan van den Ende — Wed, 12 Mar 2008 08:43:08 GMT

Paul,

The Free List size is a bit of a hidden presence these days!

If you have XFC activated (normal thing from V7 onward) then the available (otherwise unused) memory, upon release was formerly given to the free list, but nowadays any once-accessed disk file stays mapped in the XFC cache. (well, currently forgetting all gory details).
And this helps performance enormously, but hides the memory not currently in use.

Way out the best you can do, is follow Kalle's advise, and let AUTOGEN handle it.
Tweaking by MODPARAMS is possible, but DOES require understanding of the various memory influencing params.

The System Management Manual does provide a good overview, and does handle the relations between various params.

hth

Proost.

Have one on me.

jpe

Re: How do I increase free list size

Paul cotton — Wed, 12 Mar 2008 09:02:17 GMT

Paul,

just buy more memory... :-)

There are a lot of sysgen parameters around the freelist size and its treatment by VMS.

Unless you are a very experenced system administrator I would suggest to use the AUTOGEN facility to to the treaking.

After some days of 'normal' system load do a
$ @SYS$UPDATE:AUTOGEN SAVPARAMS TESTFILES
and review the SYS$SYSTEM:AGEN$PARAMS.REPORT.

If no errors or severe warnings were present, redo the run with
$ @SYS$UPDATE:AUTOGEN SAVPARAMS SETPARAMS
and perform a reboot at some convient time.

And read the manuals, as usual.

Karl

thanks for your response. I neglected to include quite a bit of detail on my original post. Basically the system in question is a DS25 at one of our sites on Malaysia, that I've recently been asked to manage - having previously been left completely unattended
(in terms of system/performance management) but still supporting live userbase.

The modparams.dat on this system was completely unpopulated until I looked at it this week. I increased the values of freelim, growlim & borrowlim (to all have the same value- 498) and increased freegoal to be 6 times this value and also applied changes to system yesterday using autogen.

The system was rebooted this morning but the free list size is still set at the original value of 512K (system has 4Gb of physical memory). Could this be due to the fact that autogen hasn't been run long enough to generate any meaningful feedback data and therefore changes I made won't filter through until autogen has been run for a few more days (and system rebooted again?)

Re: How do I increase free list size

Volker Halle — Wed, 12 Mar 2008 09:02:57 GMT

Paul,

please explain, what problem you are seeing or what you are trying to achieve.

Volker.

Re: How do I increase free list size

Wim Van den Wyngaert — Wed, 12 Mar 2008 09:16:29 GMT

Re: How do I increase free list size

Paul cotton — Wed, 12 Mar 2008 09:22:55 GMT

Paul,

please explain, what problem you are seeing or what you are trying to achieve.

Volker

Well the issue that is being reported to me is that the system is hanging with 50 users connected. I then noticed that free list becomes exhausted at about the same time
as users report the system hang.

Re: How do I increase free list size

Paul cotton — Wed, 12 Mar 2008 09:31:57 GMT

It's been a long time but
@SYS$UPDATE:AUTOGEN SAVPARAMS SETPARAMS
aborts when there are errors. And thus the setparams is not done.
You need to do @SYS$UPDATE:AUTOGEN SETPARAMS
by hand again.

Fwiw

Wim

Wim,

The autogen changes I made yesterday did get applied to the system but have not resulted in the free page size increasing.

regards
paul

Re: How do I increase free list size

Wim Van den Wyngaert — Wed, 12 Mar 2008 10:01:01 GMT

This gives some info about the interaction of xfc and the free list.
http://unix.derkeiler.com/Newsgroups/comp.os.vms/2004-09/2224.html

Wim

Re: How do I increase free list size

Hein van den Heuvel — Wed, 12 Mar 2008 10:22:14 GMT

Re: How do I increase free list size

Paul cotton — Wed, 12 Mar 2008 14:10:13 GMT

A picture speaks a thousand words, even if it is a picture of words....

Please attach a .TXT file with the output for $SHOW MEM/FULL when the system was nicely used, SYSGEN SHOW /MAJOR and toss in a SHOW SYSTEM or MONI SYSTEM (per process memory) output while collecting.

It is quiet possible there simply is not enough physical memory.

And focus on history.
You suggest is worked fine unattended. Well, stop attending!

What else changed? More users?

Were the working set params tweaked such that now memory is overcommited?
Was a dababase cache tweaked, making it use more memory?

Hein

I should point out that previously this system only hosted rdb databases but was recently upgraded to support oracle and rdb server (+ apparently system performance
was never that good in the first place)

I think the physical memory constraint on this box is, as you suggested, preventing me from increasing the free page list. I have however increased the modified page list on this system as I believe that if free list size becomes exhausted it can aquire unused pages from the modified page list ?

regards
Paul.

The attached file contains the output you requested.

Re: How do I increase free list size

Volker Halle — Wed, 12 Mar 2008 14:24:03 GMT

Paul,

please do not repeat the previous text in your replies. This wastes a lot of space on the screen, if looking at the whole topic.

The memory data shown in your attachment shows 347795 free pages = 2.8 GB (note: ALPHA 8kb pages !) of 4 GB of physical memory.

The pagefile space is not used at all, but it seems rather small (325 MB).

What do you do if the system hangs ? Just restart it ? Maybe consider to force a crash:

press halt button
>>> crash

Then you can look at the dump to figure out, what's really wrong...

Volker.

Re: How do I increase free list size

Hein van den Heuvel — Thu, 13 Mar 2008 01:38:10 GMT

>> The attached file contains the output you requested.

It's a fine dry-run.
But the the system was entirely idle.
I indicated "when the system was nicely used".
Maybe I should have written 'badly used' instead of 'nicely' :-).

It does show something big already though.
It shows 1GB set aside for the new Oracle install.
On 4 GB that would rate as 'significant impact'
"reserved Memory" is the optimal way to use memory... if you have enough.
But is totally, extremely, inflexible.
It is set aside for one purpose and one purpose only and firmly suggest you know better then OpenVMS how to utilize memory.
The very fact that you opened this topic suggest that there is not enough knowledge to make that call.

Tell those Oracle folks to back off!
Have them provide the Proof that they need the memory, and be ready to add more.

They allocated 1.00 GB. Right there that tells me they just picked a 'nice round number' and are possibly clueless. If 0.80 GB is enough, then that's 200MB more for you free page list!

Make them do their homework and figure out how much memory is truly needed to make the Oracle part of the application work reasonably well.

If they claim 'it will go slower' then you respond 'really? Slower than "the system is hanging with 50 users connected."?'

Also, How much is your time worth, and the end user satifaction worth, compared to the price of increasing memory?!

Good luck!

Hope this helps some,
Hein van den Heuvel (at gmail dot com)
HvdH Performance Consulting

Re: How do I increase free list size

Jur van der Burg — Thu, 13 Mar 2008 07:09:32 GMT

You're not using XFC but the old VIOC cache (VCC_FLAGS is not set to 2). Why? XFC is way better. What VMS version are we talking about?

And why do you want a big freelist? You obviously need some free memory, but in essence free memory is wasted memory.

Install T4 on the system and let it run during prime time, that will give you someting to look at. Also, tinkering with memory parameters like freegoal and such makes no sense if you don't know the workload. Best is to leave them alone and let autogen do the job. Nowadays there's hardly anything you can gain with those parameters, except in special cases, but then you really have to know what you do, and you have to know the applications behavior.

Jur.

Re: How do I increase free list size

Willem Grooters — Thu, 13 Mar 2008 07:18:58 GMT

The problem is: If 50 users access the system, it hangs.
It wouldn't be caused by exhaustion of free space alone (that's what Virtual Memory System is all about: Using (far) more memory that is physical present in your system).

I concur with Hein: Login (as admin), have you users do their job, and start monitoring the system when 40, or 45, have logged in, add more users until the system hangs. Check available memory - and, most important, pagefile use.

If your free memory pool gets exhausted, the system will try to free pages from the mdoified page list by relocating the contents into the pagefile. If that get's exhausted, you may encounter a situation know as thrashing where the system will seem to hang - for all users.

If you could supply a SHOW MEMORY output just before this happens (say: when 48 users have logged in), that would show a better indication.

Since others have already indicated that your pagefile is rather small, it may be worthwhile to extend both page- and swapspace on disk (adding a new pagefile is easy and can be done without rebooting the system). But this can only be p[roven by the asked output.

Another possibility is that the software you use may cause a problem. What if the software that your users use, is accessing the Oracle dataase and exhasuting the Oracle dataspace?

Re: How do I increase free list size

The Brit — Thu, 13 Mar 2008 13:19:06 GMT

Remind me, you are running OpenVMS 7.2, but did you say whether you are on VAX or Alpha.

Other useful information would be the values of the PQL parameters.

vis.

sysgen show pql

I noticed that WSMAX is set to almost 1M pages, so it is quite important to know what the values of WSEXTENT and WSQUOTA are.

It is possible that processes are hogging the available memory as they login, and are not giving it back.

There is no automatic reclaimation taking place, (PFRATL = 0). Try turning this on.
(although it may not help since you dont seem to be doing any significant paging)

If you do turn it on (set pfratl > 0), suggested values are: (all dynamic)

pfratl = 1
pfrath = 10
wsinc = 2048
wsdec = 512

The fact that you are not paging may be a reflection of the fact that the processes which are "IN", are functioning with large Working Sets.

Just a couple of thoughts.

Dave

Re: How do I increase free list size

Paul cotton — Fri, 14 Mar 2008 10:36:22 GMT

Good morning,

I would just like to thank everyone for the feedback they've provided me on this issue to-date. I apologise for taking so long in responding to everyone but since posting my last update yesterday have been partly offsite and am playing catch-up with various things today

I may not get an opportunity to respond to each of your posts individually (but I'll try to respond to those which i feel are relevant/have requested feedback). In tne meantime I've tried to awward points as fairly as possible.

In terms of the actual issue i reported I will leave it open until next monday before deciding whether the thread can now be closed
Basically next monday is the earliest that malaysia can arrange to have live users reconnect to that system - currently using a backup system instead).

Also since reading your posts I've discovered that the oracle alert file on the DS25 system is indicating that the memory reserved for Oracle is set to higher value than required , which does indicate that Hein was correct - (so thanks for that feedback especially Hein), and that oracle are essentially tinkering with the sizing rather than actually calculate a correct value.

What I have also noticed is that the users working set quotas are set quite high so have enabled awsa and hopefully they'll get reclaimed if necessary. I'm also increasing the size of the pagefile
so that hopefully free page list will now be able to expand by transferring contents of modified page list onto the pagefile if required (I had increased mpw_hilimit a few days ago for this very reason but not had a chance to test whether this provided free page list with additional memory yet.

I'll try and come back to those people that have requested feednback from me but if not then I'll post an update next monday.. thanks for your time.

regards
Paul

Re: How do I increase free list size

Paul cotton — Mon, 17 Mar 2008 10:44:02 GMT

Good morning

I may have been a little bit over enthusiastic in awarding points on this posting. This is my the first posting on this forum, and having just read one of the alert notification emails from HP i now understand the way points should be awarded!

This issue is currently still open as I'm waiting on the guys in Malaysia to complete some associated tasks before deciding
whether this call can now be closed.

If the system continues to hang then I'll capture the show mem/full output + anything which looks relevant and post it on my next update.

Re: How do I increase free list size

Guenther Froehlin — Mon, 17 Mar 2008 15:22:46 GMT

Paul,

why is your focus on increasing FREELIM? It would make things worse by keeping an artificially long free page list. Let processes get to free pages.

When the system "hangs" what "hangs"? Certain applications?

You need to look at "SHOW SYSTEM" for any wait state. Like RWCSC, RWMPB... My wild guess is that the system ran out of page file space and processes got stuck in RWMPB (resource wait modify page writer busy).

A "SHOW MEMORY/FILES" from the loaded system would give an idea about the page file sizes.

/Guenther

Re: How do I increase free list size

Hoff — Mon, 17 Mar 2008 18:45:38 GMT

Free memory is (by definition) wasted memory.

The old Free Memory "stuff" changed at V7.2, with the advent of XFC. As has been mentioned here in the thread.

Some (now-old) performance-monitoring tools (erroneously) report configuration errors starting at V7.2 due to the changes in how system physical memory was utilized.

The points system serves as a distraction, and one of (many) ill-conceived and disruptive (and buggy) features of the user interface used here in ITRC.