topic Re: Resident vs Virtual Memory in Operating System - HP-UX

Resident vs Virtual Memory

support_5 — Tue, 04 Oct 2005 01:28:46 GMT

Hi all,

I am looking at Glance and notice that there are some processes with enormous amounts of "Virtual Memory", while at the same time having very low "Resident Memory".

Eg:
Process Name Res Mem Virt Mem
ora_pmon_txcxadb 8.7MB 795.8MB

What's up with that? That doesn't sound right??

Or this one:
Process Name Res Mem Virt Mem
java 42.9MB 712.6MB

That doesn't seem right to me.

Can someone please give suggestions as to why the huge discrepancy from what one might typically expect?

Can folk please shed some light on how resident and virtual memory impact physical and swap memory. (we do not have pseudo swap turned on, but do have 30GB of swap memory for a system with 14GB physical memory)

Thank you

- Andrew Gray

Re: Resident vs Virtual Memory

Arunvijai_4 — Tue, 04 Oct 2005 01:32:45 GMT

A good thread to read,

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=463908

-Arun

Re: Resident vs Virtual Memory

Arunvijai_4 — Tue, 04 Oct 2005 01:56:29 GMT

Resident Memory

This column reflects the amount of physical memory currently allocated to each process. This is also known as the "resident set size" or RSS. A process can have a large amount of virtual memory allocated (as indicated by the SIZE column) but still be using very little physical memory.

Re: Resident vs Virtual Memory

Muthukumar_5 — Tue, 04 Oct 2005 02:22:05 GMT

A good explanation:

VIRT -- Virtual Image (kb)
The total amount of virtual memory used by the task. It includes
all code, data and shared libraries plus pages that have been
swapped out.

VIRT = SWAP + RES.

SWAP -- Swapped size (kb)
The swapped out portion of a task's total virtual memory image.

RES -- Resident size (kb)
The non-swapped physical memory a task has used.

RES = CODE + DATA.

CODE -- Code size (kb)
The amount of physical memory devoted to executable code, also
known as the 'text resident set' size or TRS.

DATA -- Data+Stack size (kb)
The amount of physical memory devoted to other than executable
code, also known as the 'data resident set' size or DRS.

SHR -- Shared Mem size (kb)
The amount of shared memory used by a task. It simply reflects
memory that could be potentially shared with other processes.

hth.

Re: Resident vs Virtual Memory

Muthukumar_5 — Tue, 04 Oct 2005 02:23:17 GMT

Memory management document:

http://docs.hp.com/en/1218/mem_mgt.html

hth.

Re: Resident vs Virtual Memory

Muthukumar_5 — Tue, 04 Oct 2005 02:24:25 GMT

A good link to give information more on resident and virtual.

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=712845

You can resident and virual information for a process with top utility using RES and SIZE fields.

hth.

Re: Resident vs Virtual Memory

Arunvijai_4 — Tue, 04 Oct 2005 02:25:38 GMT

http://docs.hp.com/en/5965-4641/ch01s02.html

[OVERVIEW OF PHYSICAL AND VIRTUAL MEMORY]
A good document to get an overview of memory.

-Arun

Re: Resident vs Virtual Memory

Steve Steel — Tue, 04 Oct 2005 02:29:38 GMT

Hi

2 good urls

http://www.hp.com/products1/unix/java/infolibrary/tools/

ftp://eh:spear9@hprc.external.hp.com/memory.htm

It is explained there with options

The first one is mainly based on java performance analysis ut still valid

Steve Steel

Re: Resident vs Virtual Memory

morganelan — Tue, 04 Oct 2005 04:25:47 GMT

The RSS (resident set size) shown by ps is not a valid indication of PGA size. It includes the SGA (db_block_buffers & shared_pool_size) and is sensitive to memory pressure on the system as well as to PGA size.