buffer cache size

[Larry Basford]

I'm looking at a Global swap space nearly full.
This system is running 29 Oracle instances.
can I set dbc_max_pct to 5 to get some usable memory back.

It has 15 GB and is set to 25% now.
That is 3GB buffer cache now.


swapinfo -tam
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 1024 0 1024 0% 0 - 1 /dev/vg00/lvol2
reserve - 1024 -1024
memory 12059 11410 649 95%
total 13083 12434 649 95% - 0 -


hpmem
HP-UX hp4 B.11.00 A 9000/800 608369393 two-user license
CPU Count: 4
CPU Speed: 550 MHz
CPU HW Support: 64-bit
Kernel Support: 64-bit
RAM Size: 15360 MB
bufpages: 3840 MB
maxuprc: 2898
maxvgs: 10
maxfiles: 320
max_thread_proc: 64
nfile: 118114
nflock: 8192
nproc: 3220
ninode: 4468
shmmax: 1073741824
shmmni: 200
dbc_max_pct: 25

[A. Clay Stephenson · Accepted solution]

In a word, yes. You may find it better to run a fixed buffer cache by setting bufpages to a non-zero value. I would limit your buffer cache to something near 800MB (bufpages=204800). 15GB is not a whole lot of memory for this many instances so you would be wise to reduce the sizes of the SGA's in the lightly used instances especially.

[G. Vrijhoeven]

Hi,

Buffercache is set up dynamicly between dbc_max_pct en dbc_min_pct. The min defaults to 5. It is possible to set both dbc_max_pct and dbc_min_pct to the same value, 5 for example, and create a kernel that uses exactly that percentage of physical memory for the buffer cache, regardless of the size of physical memory.

You could check these links for more info:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=467288

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=289087

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=230807

HTH,

Gideon

[Hai Nguyen_1]

Larry,

You certainly can and should reduce the max down to at least 10% since Oracle instances already request their own memory spaces.

Hai

[Larry Basford]

Thanks for all the info.
I'm going with the bufpages=204800

That way when we cram more memory in this pig it will be a fixed value.

The tuning guide answered a lot of querstions.

[hpuxrox]

Last I checked anything over 1G of buffer cache is not supported.

Anyways, if your array is caching their is no need for 3G of system cache.