excessive swapping during rman backups on Linux 2.6

From: NetComrade <netcomradeNSPAM_at_bookexchange.net>
Date: Mon, 15 Jan 2007 01:43:02 -0500
Message-ID: <2j5mq21j9ikencpkdejc7gl46cc0c7hlcj@4ax.com>

We have a customer that recently have migrated to Linux from Windows. The database is 9.2.7.the os is redhat 4.0 We noticed that whenever there is a level 0 backup running, the machine starts swapping, load jumps, and it becomes unresponsive at times. The db has a 'max sga' set at 3G and a pga_target of 500m. The machine has 8G of ram (one db on the machine, small data processing app). The number of connections is around a hundred.. ---There should be enough memory resources for this db

There is a metalink note 360402.1 describing out situation, and it basically suggests adjusting some kernel settings to make kernel reserve less memory for FS caching. Unfortunately, these parameters (/proc/sys/vm/pagecache, /proc/sys/vm/freepages /proc/sys/vm/buffermem no longer exist in kernel 2.6 ). Besides going 'directio' (customer had mixed results during testing), any other suggestion(s)?

sar output during levl0:

kernel.sem = 1000        32000   100      128
11:40:02 PM     96.67    108.06
11:50:08 PM    145.22     62.10
Average:         1.96      1.20
12:00:01 AM  pswpin/s pswpout/s
12:10:05 AM    269.83    176.13
12:20:01 AM    462.24    142.03
12:30:22 AM    259.53    108.06
12:40:12 AM    283.60    132.79
12:50:01 AM    343.39     88.04
01:00:01 AM    352.47    152.02
01:10:01 AM    460.48    218.64
01:20:03 AM    215.97     99.27
01:30:01 AM    305.85    105.11
01:40:02 AM    232.30    112.40
01:50:02 AM    327.64    131.49
02:00:01 AM    247.68     88.48
02:10:03 AM    157.55     67.92
02:20:05 AM    223.74     90.92
02:30:01 AM    129.21     44.13
02:40:02 AM    140.25     61.81
02:50:01 AM     17.83      0.00
03:00:01 AM     15.00      0.33
03:10:01 AM      3.73      0.00
03:20:01 AM      2.75      0.00
03:30:01 AM      1.02      0.00
03:40:01 AM      0.70      0.00
03:50:01 AM      0.38      0.00
04:00:01 AM      0.89      0.00
04:10:01 AM     34.69      0.00

# free
             total       used       free     shared    buffers
cached
Mem:       8165948    8148012      17936          0       4016

1109552
-/+ buffers/cache: 7034444 1131504 Swap: 16779884 1224096 15555788

sysctl:
fs.file-max = 65536

kernel.shmall = 1572864
kernel.sem = 1000        32000   100      128
kernel.shmmax = 6442450944

net.ipv4.ip_local_port_range = 1024 65000 vm.nr_hugepages=3100

.......
We run Oracle 9iR2,10gR1/2 on RH4/RH3 and Solaris 10 (Sparc) remove NSPAM to email Received on Mon Jan 15 2007 - 00:43:02 CST