Re: Memory problems, Oracle 10, Win 2003 (32 bit)


"mike.reid" <chmonkey@xxxxxxxxx> wrote in message
news:9385d505-f61b-49eb-ac09-b072ebffd8b6@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jun 15, 1:30 pm, "gym dot scuba dot kennedy at gmail"
<kenned...@xxxxxxxxxxx> wrote:
"mike.reid" <chmon...@xxxxxxxxx> wrote in message

news:5503e537-f8f0-44ad-8fb8-24d4f4924d87@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I was hoping to get some assistance from the group....

I am working with a client who is running into some memory problems
with theirOracledatabase.

Now I am not an expert by a long shot, but the application vendor has
told us that their rule of thumb is to always force a pagefile that is
2.5 times the physical memory (so 10gb in this case).

My understanding on the subject was that becauseOracleis
"Opportunistic" with its memory usage that you actually want to pretty
much disable the pagefile altogether so thatOracledoes use it.

Just taking a look at the server seems to tell thatOracleis using
about 800mb of physical and 1.7gb total. Is it reasonable in your
opinion to run a test and disable the pagefile all together?

Any help that anyone can give me would be greatly appreciated!

Mike

I am not sure what the problem is. You sayOracleis using about half the
memory in the machine. You say you have memory problems. What is the
memory problem? Very unclear what problem you are having.

On Windows machines if you allocate more memory than you have RAM then
you
will swap some of the memory pages to disk (in the pagefile) If you
rarely
access that memory than things might not be too bad. If you keep
accessing
memory that has been swapped to disk - and force other pages to be
written
to disk - then you can have the machine grind to a halt as it tries to
use
disk as if it were RAM. This is true ofOracleusing the memory or Word or
any program.

Our crystal balls are in the shop, you need to enlighten us as to what is
going on more specificaly. My first bit of advice would be to NOT
disable
the pagefile.
Jim

Thanks for the reply Jim. I agree and I apologize for not being more
descriptive.

- 1gb database
- 4gb physical memory, 10gb pagefile
- RAID 5 (shared with OS, DB Logs and DB) Write back cache disabled
- 20 or so users connecting from Terminal Server to DB server, mostly
direct calls, some stored procedures

There are some obvious performance improvements to be had with this
setup. I am not the application vendor, but am just trying to give a
hand. Performance has recently ground to a halt. There are
expectations to double the users of the system, the application
developers are saying that a new server must be purchased now (which
they do actually need a new sever for other reasons, so I'm not too
fussed about that). The first thing that we have been told to do is
create a pagefile that is 20gb in size (8gb mem on the new server x
2.5).

The question that I have is (and I do not have a lot of experience
with Oracle in general):

- Don't you want Oracle to _never_ page to disk? The fact that there
is 4gb (physical) memory in the old server and that Oracle was only
using 800mb physical, but 1.7gb total (at the time I was on the
thing), then is perhaps a course of action to disable the pagefile to
force Oracle to use only physical memory? As a test at least?

Again, I apologize for the lack of information. I hope this is
better.

Thanks
Mike
Mike,
1. Everyone should stop proposing solutions.
2. Determine what the problem is.
3. Measure the largest bottleneck.
4. Consider if you removed that bottleneck then how much would performance
improve?

For example, I worked on a system written in an interpreted scripting
language. The claim by the people who wanted it in C was that C was faster
and solve all the performance problems. (never mind it would have taken 10x
longer to write the system in C and that we didn't have but a few people who
could write quality C code.) The main concern was the calculation time for
a pension benefit estimate. On the base system the calculation took 6
seconds. (This was the mid 1980's) The scripting language did have a
profiler. So I turned ont he profiler and did the base calculation. I saw
that about half the time for the calculation was retrieving data to do the
calculation. Therefore if we did the calculation in C and if the new time
for the calculation part was 0 seconds then at best a calculation would take
3 seconds. (the database retrieval code was already in C and using bind
variables, reusing cursors etc. so it was highly optimized)

The moral of the story is that you need to understand where the time is
being taken.

At another job we were able to get 1,500 users running against Oracle with
Oracle running on a Windows NT machine. (4 pentium pro 200 mghz CPUs w/ 4
gig of ram and 20 disks in a stripe 4 scsi controllers) With an automated
randomized workflow. (simulating a Dr's office, a really big dr's office) We
could not get more users on because NT has a per process thread limit and
Oracle (8i) on NT used threads for dedicated users. How did we do it? We
had a highly optimized application. We looked at where our bottlenecks were
and took care of the largest ones first. We read the Oracle Application
Developer's guide and used the performance techniques in the documentation.

So take 1 example of a performance problem. It must be specific and
reproducable. Investigate what in that process is taking so long. Look at
the 1 thing that is taking so long and ask yourself if I eliminated that
would the performance problem go away? How about the top 2 things?

If you think it is a memory issue then is the machine swapping? Windows has
a bunch of performance counters which ones are outside reasonable bounds.
(disk queue lengths?)

I'm sorry Mike, but it sounds like a bunch of people just want to throw
money at a problem before understanding what the problem is. My bet is if
they do the problem will not be solved and they will be out the money. I'm
not against buying a new server especially if the one there is at the end of
life. One thought did cross my mind. I bet they have an active virus
scanner running on that machine. If so turn the damn thing off or at least
exclude the whole Oracle home from it.
Jim


.

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