topic Re: cache memory utilization high. in Operating System - HP-UX

cache memory utilization high.

gb karki — Thu, 28 Jan 2010 09:17:15 GMT

Hi expert,

We have HP-UX 11.31 system with 36GB physical memory and by default 50% of phycical memory is taken by cache memory.

Problem is here, cache memory is used continuosly 16.5 GB.

oracle team has given 12 GB for oracle after that memory is reaching 100%.

you can see the filecache values.

root@st1ciwtn:/ # kctune filecache_max
Tunable Value Expression Changes
filecache_max 18359316480 Default Auto

root@st1ciwtn:/ # kctune filecache_min
Tunable Value Expression Changes
filecache_min 1835929600 Default Auto

root@st1ciwtn:/ # kcusage filecache_max
Tunable Usage / Setting
=============================================
filecache_max 17660841984 / 18359316480
root@st1ciwtn:/ #

glance:-

CPU Util SSU U | 6% 7% 12%
Disk Util F F | 5% 7% 21%
Mem Util S SU UF F |100% 100% 100%
Networkil U UR R | 55% 55% 55%

Total VM : 17.2gb Sys Mem : 5.2gb User Mem: 14.2gb Phys Mem : 36.0gb
Active VM: 6.8gb Buf Cache: 3mb Free Mem: 85mb FileCache: 16.4gb

========================

root@st1ciwtn:/ # kctune maxdsiz
Tunable Value Expression Changes
maxdsiz 1073741824 1GB Immed
root@st1ciwtn:/ # ulimit -a
time(seconds) unlimited
file(blocks) unlimited
data(kbytes) 1048576
stack(kbytes) 131072
memory(kbytes) unlimited
coredump(blocks) 4194303
nofiles(descriptors) 2048
root@st1ciwtn:/ #
=========================

Can you please suggest me? what are the thing do i need to change for proper utilization cache memory or physical memory.

Regards
GB

Re: cache memory utilization high.

Fabio Ettore — Thu, 28 Jan 2010 09:42:17 GMT

Hi,

Oracle systems can usually have a Buffer Cache (in HP-UX 11.31 there's UFC, Unified File Cache) small, so definitely you could consider to decrease filecache_max to a lower value than 50% (man filecache_max).

You can do that with no reboot, however when decreasing Buffer Cache which is currently used I usually prefer to reboot the system.

HTH.

Best regards,
Fabio

Re: cache memory utilization high.

Kapil Jha — Thu, 28 Jan 2010 09:43:03 GMT

Hi Karki,

How are you?
the first thing you should check is
dbc_min_pct and dbc_max_pct you should fix these values.
Seems currently you have dbc_max_pct ~ 50
so better you try to reduce this and check.

BR,
Kapil+

Re: cache memory utilization high.

gb karki — Thu, 28 Jan 2010 09:57:14 GMT

Hi Fabio,

Thank you,

filecache_max is Auto then why we need to set the lower value.

one more thing, yesterday we have increased physical memory and oracle team has also increased oracle memory to 12 GB.

but they have not increased maxdsiz values.

current value is 1 GB.

can you suggest regarding maxdsiz?

Kapil,

I'm fine.

that parameters are available in 11.23 or below.

filecache_max and filecache_min is available in 11.31.

Thanks
GB

Re: cache memory utilization high.

Dennis Handly — Thu, 28 Jan 2010 10:11:08 GMT

>physical memory is taken by cache memory.

(In order to prevent confusion, you should say "file cache" or "buffer cache", otherwise you could be confused with CPU cache.)

>cache memory is used continuously 16.5 GB.

As Fabio said, you should reduce it.

>filecache_max is Auto then why we need to set the lower value?

Probably HP-UX doesn't know what Oracle is doing? Or that Oracle can make better use of that memory?

>they have not increased maxdsiz values. current value is 1 GB. can you suggest regarding maxdsiz?

Why would you need to make it bigger? Are your applications running out of heap space?

Re: cache memory utilization high.

Venkatesh BL — Thu, 28 Jan 2010 10:35:02 GMT

Looks like you are trying to do something without knowing what it is.

If you want file cache to use less of your RAM, reduce it (filecache_max). 'Auto' setting may take longer to cut down the value.

Re: cache memory utilization high.

gb karki — Thu, 28 Jan 2010 10:37:34 GMT

Hi Dennis,

Oracle team are getting below errors, thats why we are in loking for parameters.

get the error "ORA-04030: out of process memory when trying to allocate nn bytes".

Thanks
Karki

Re: cache memory utilization high.

Fabio Ettore — Thu, 28 Jan 2010 10:48:28 GMT

Hi,

Oracle systems don't need big System Buffer Cache. I'd avoid to give more details here, you'll find tons of discussions around.
Definitely you can safely consider to reduce filecache_max, and in general it isn't usually good to keep it at default 50%. With such settings the memory will be available for User Memory only for 50%. Reducing filecache_max means having much more memory available for User side.
I think a good value for filecache_max in your situation might be under the 10%.

Regarding maxdsiz, I wouldn't change it if you don't have specific issues having it at 1 Gb.

HTH.

Best regards,
Fabio

Re: cache memory utilization high.

Kapil Jha — Fri, 29 Jan 2010 03:02:33 GMT

file cache or buffer cache are same thing except with different name [ I doono why they used to change names ]

Well for you the error you getting ORA-4030 is becuase its not able to allocate memory, it has nothing to do with maxdsize.
If there would have been a issue with maxdsiz you error might have been smthing like.....can not allocate required memory chunk.
maxdsiz(5).
So best thing to do right now is to reduce the buffer cache and check sysem performance.

BR,
Kapil+

Re: cache memory utilization high.

Dennis Handly — Fri, 29 Jan 2010 12:17:24 GMT

>get the error "ORA-04030: out of process memory when trying to allocate nn bytes".

What was "nn"? You should be looking at top to see how big the process is getting. If close to 1 Gb, then you need to make maxdsiz and if 64 bit, maxdsiz_64bit.

But Kapil says there is a different error message for that??

Re: cache memory utilization high.

Dennis Handly — Fri, 29 Jan 2010 12:31:22 GMT

>Kapil: file cache or buffer cache are same thing except with different name [I doono why they used to change names]

They aren't really exactly the same. The Unified file cache has one cache for both user I/O and memory manager I/O.

The buffer cache only deals with user I/O.

Re: cache memory utilization high.

gb karki — Fri, 29 Jan 2010 15:32:32 GMT

Thanks Kapil/Dennis,

After change the filecache_max values, we are in better position.

Thanks
Karki