IIS 6 app pool memory usage questions

1. is it normal for an app pool to use a lot more virtual memory than RAM,
say 15 times as much?

2. what can I expect the overhead per application pool to be? reason I as is
I am wondering how many app pools I can have on a server.

3. where can I find benchmarks on how much memory an app should use?

I am looking to break up application into their own app pools to isolate
them from each other, but in doing so I noticed that each app pool that uses
the 1.1 framework is consuming over 400 megs in virtual memory
apps using the 2.0 framework use up over 500 megs of virtual memory, which
is higher than the default for app pool recycling based on memory usage.

I am trying to find out if that is normal, but haven't had much luck yet.
thanks

Pat
Tue Mar 14 12:32:26 CST 2006

1) How are you measuring memory usage. The 2 counters that really matter
are (in PerfMon) Virtual Memory Allocated & Private Bytes. You can't
actually see the RAM used. VM Used will always be greater than private
bytes.

2) Depends to some degree on how much stuff you are loading into the pool.
On a 32bit system, generally < 100; and most are 20-->50, complex ones may
be <10.

3) It will depend entirely on the app itself. Perfmon:Process:Private Bytes
is the best indicator of the actual memory footprint. Virtual Memory
allocated may not actually be 'backed' by RAM/Page File unless there is data
actually put there. Windows Internals 4th Edition goes into great detail on
memory and understanding how it is used.


Pat




"jason" <jason@discussions.microsoft.com> wrote in message
news:960EB4E0-FAF5-47F4-A746-49D6D99AD332@microsoft.com...
> 1. is it normal for an app pool to use a lot more virtual memory than RAM,
> say 15 times as much?
>
> 2. what can I expect the overhead per application pool to be? reason I as
> is
> I am wondering how many app pools I can have on a server.
>
> 3. where can I find benchmarks on how much memory an app should use?
>
> I am looking to break up application into their own app pools to isolate
> them from each other, but in doing so I noticed that each app pool that
> uses
> the 1.1 framework is consuming over 400 megs in virtual memory
> apps using the 2.0 framework use up over 500 megs of virtual memory, which
> is higher than the default for app pool recycling based on memory usage.
>
> I am trying to find out if that is normal, but haven't had much luck yet.
> thanks

DaveK
Tue Mar 14 12:51:26 CST 2006

1. Only if you are running a large application on a server with very little
memory

2. You can have as many as you like as long as your users are satisfied with
the web sites performance.

3. There is no answer to that question because every application is different.

There is no such thing as "normal". I have 26 app pools on my main server.
The largest w3wp is using 400 meg, and I count 13 under 50 meg.

If your app pool is 15 times bigger than physical RAM, then you most likely
have a problem. Try to isolate which web site or directory that is using the
most memory.

For ASP pages, check that all creatobject calls use server.createobject.
Make sure that the object is set to nothing before the page exits. For adodb
connections, make sure thay they are closed.

For .Net apps, check the bin directories of each to see if your developers
are using common dll's. If they are, you may be getting multiple copies
loaded into memory. Register shared code in the GAC.

Good luck.

jason
Tue Mar 14 15:09:28 CST 2006

I am using pefmon counter to monitor virtual bytes

I look at task manager, that maps to RAM

The two map directly to the memory based recycling in IIS app pools. at
least all my testing indicates this.

I am using 2 test apps, both very simple that do nothing more than to store
a test string into session state
one is using 1.1 framework, the other is using the 2.0

what i see based on these counters, is that storing a short string in 1.1
used about 30 megs or RAM and 440 megs of virtual
on 2.0 its about 30 megs of RAM and 540 megs of virtual.

when i look at other apps i see various numbers but nearly always over 400
megs of virtual memory.




"Pat [MSFT]" wrote:

> 1) How are you measuring memory usage. The 2 counters that really matter
> are (in PerfMon) Virtual Memory Allocated & Private Bytes. You can't
> actually see the RAM used. VM Used will always be greater than private
> bytes.
>
> 2) Depends to some degree on how much stuff you are loading into the pool.
> On a 32bit system, generally < 100; and most are 20-->50, complex ones may
> be <10.
>
> 3) It will depend entirely on the app itself. Perfmon:Process:Private Bytes
> is the best indicator of the actual memory footprint. Virtual Memory
> allocated may not actually be 'backed' by RAM/Page File unless there is data
> actually put there. Windows Internals 4th Edition goes into great detail on
> memory and understanding how it is used.
>
>
> Pat
>
>
>
>
> "jason" <jason@discussions.microsoft.com> wrote in message
> news:960EB4E0-FAF5-47F4-A746-49D6D99AD332@microsoft.com...
> > 1. is it normal for an app pool to use a lot more virtual memory than RAM,
> > say 15 times as much?
> >
> > 2. what can I expect the overhead per application pool to be? reason I as
> > is
> > I am wondering how many app pools I can have on a server.
> >
> > 3. where can I find benchmarks on how much memory an app should use?
> >
> > I am looking to break up application into their own app pools to isolate
> > them from each other, but in doing so I noticed that each app pool that
> > uses
> > the 1.1 framework is consuming over 400 megs in virtual memory
> > apps using the 2.0 framework use up over 500 megs of virtual memory, which
> > is higher than the default for app pool recycling based on memory usage.
> >
> > I am trying to find out if that is normal, but haven't had much luck yet.
> > thanks
>
>
>

Pat
Wed Mar 15 09:07:51 CST 2006

The string itself doesn't take that much - when you hit a page for the 1st
time, all of the ancillary structures and libraries get loaded up - which
bumps the VM usage. .Net leverages multiple heaps - small strings are
actually placed in Heap0 for garbage collection. So, whether a string is 8
bytes or 40k, the initial hit initiallizes all of the heaps, spawns worker
threads (256k per thread), etc. You can think of VM allocations as sparse
arrays - they tend to be oversized on allocation and are filled in over
time. Also, from the OS perspective, VM allocations tend to overstate the
issue. For example, NTDLL.DLL is the first dll loaded into every process -
and from a purely VM perspective space for the dll will be allocated from
every process. But the OS only actually loads one copy and remaps it
multiple times. So the actual amount of physical memory needed is much
smaller than adding up VM allocations.

Private Bytes gives you a better idea of memory actually used - though
w/.Net (or Java) you will tend to see stair steps b/c the memory manager
tends to preallocate large chunks. This ignores bytes that are remapped
from the OS. So, you don't get the double count. So, PB will give you an
idea of the resource footprint that adding another pool will have.


Pat



"jason" <jason@discussions.microsoft.com> wrote in message
news:F85A4EBB-CD35-44D4-9AD3-9384A99313BA@microsoft.com...
>I am using pefmon counter to monitor virtual bytes
>
> I look at task manager, that maps to RAM
>
> The two map directly to the memory based recycling in IIS app pools. at
> least all my testing indicates this.
>
> I am using 2 test apps, both very simple that do nothing more than to
> store
> a test string into session state
> one is using 1.1 framework, the other is using the 2.0
>
> what i see based on these counters, is that storing a short string in 1.1
> used about 30 megs or RAM and 440 megs of virtual
> on 2.0 its about 30 megs of RAM and 540 megs of virtual.
>
> when i look at other apps i see various numbers but nearly always over 400
> megs of virtual memory.
>
>
>
>
> "Pat [MSFT]" wrote:
>
>> 1) How are you measuring memory usage. The 2 counters that really matter
>> are (in PerfMon) Virtual Memory Allocated & Private Bytes. You can't
>> actually see the RAM used. VM Used will always be greater than private
>> bytes.
>>
>> 2) Depends to some degree on how much stuff you are loading into the
>> pool.
>> On a 32bit system, generally < 100; and most are 20-->50, complex ones
>> may
>> be <10.
>>
>> 3) It will depend entirely on the app itself. Perfmon:Process:Private
>> Bytes
>> is the best indicator of the actual memory footprint. Virtual Memory
>> allocated may not actually be 'backed' by RAM/Page File unless there is
>> data
>> actually put there. Windows Internals 4th Edition goes into great detail
>> on
>> memory and understanding how it is used.
>>
>>
>> Pat
>>
>>
>>
>>
>> "jason" <jason@discussions.microsoft.com> wrote in message
>> news:960EB4E0-FAF5-47F4-A746-49D6D99AD332@microsoft.com...
>> > 1. is it normal for an app pool to use a lot more virtual memory than
>> > RAM,
>> > say 15 times as much?
>> >
>> > 2. what can I expect the overhead per application pool to be? reason I
>> > as
>> > is
>> > I am wondering how many app pools I can have on a server.
>> >
>> > 3. where can I find benchmarks on how much memory an app should use?
>> >
>> > I am looking to break up application into their own app pools to
>> > isolate
>> > them from each other, but in doing so I noticed that each app pool that
>> > uses
>> > the 1.1 framework is consuming over 400 megs in virtual memory
>> > apps using the 2.0 framework use up over 500 megs of virtual memory,
>> > which
>> > is higher than the default for app pool recycling based on memory
>> > usage.
>> >
>> > I am trying to find out if that is normal, but haven't had much luck
>> > yet.
>> > thanks
>>
>>
>>