Red Hat ENTERPRISE LINUX 5.1 - LINUX ORACLE Quick start guide

Red Hat Enterprise
Linux 5.1
Red Hat Enterprise Linux
Oracle Tuning Guide
Tuning and optimizing performance tips and guidelines for Oracle®
9i and 10g databases on Red Hat Enterprise Linux 5, 4, 3 and 2.1

Red Hat Enterprise Linux Oracle Tuning Guide
Red Hat Enterprise Linux 5.1 Oracle 9i and 10g Tuning Guide
Tuning and optimizing performance tips and guidelines for
Oracle® 9i and 10g databases on Red Hat Enterprise Linux 5, 4, 3
and 2.1
Edition 1.4
Editor Chris Curran [email protected]
Copyright © 2007 by Red Hat, Inc.
Red Hat owns the copyright to this and all other subsequent derivative works. Werner Puschitz retains
the copyright to the original at www.puschitz.com
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This guide provides step by step instructions for tuning and optimizing Red Hat Enterprise Linux
on x86 and x86-64 platforms running Oracle®9i (32 bit or 64 bit) and Oracle®10g (32 bit or 64 bit)
standalone and RAC databases. It covers Red Hat Enterprise Linux Advanced Server 3 and 4 and the
older version 2.1.

iii
I. Tuning and Optimizing Red Hat Enterprise Linux for Oracle Database 9i and 10g 1
1. Introduction 3
2. Hardware Architectures and Linux Kernels 5
2.1. General ............................................................................................................... 5
2.2. 32 bit Architecture and the hugemem Kernel .......................................................... 5
2.3. The 64 bit Architecture ......................................................................................... 6
3. Kernel Upgrades 7
4. Kernel Boot Parameters 9
4.1. General ............................................................................................................... 9
4.2. The I/O Scheduler ................................................................................................ 9
5. Memory Usage and Page Cache 11
5.1. Checking the Memory Usage .............................................................................. 11
5.2. Tuning the Page Cache ...................................................................................... 11
6. Swap Space 13
6.1. General .............................................................................................................. 13
6.2. Checking Swap Space Size and Usage ............................................................... 14
7. Setting Shared Memory 15
7.1. Setting SHMMAX Parameter .............................................................................. 15
7.2. Setting SHMMNI Parameter ................................................................................ 16
7.3. Setting SHMALL Parameter ................................................................................ 16
7.4. Removing Shared Memory .................................................................................. 17
8. Setting Semaphores 19
8.1. The SEMMSL Parameter .................................................................................... 19
8.2. The SEMMNI Parameter ..................................................................................... 19
8.3. The SEMMNS Parameter ................................................................................... 19
8.4. The SEMOPM Parameter ................................................................................... 20
8.5. Setting Semaphore Parameters ........................................................................... 20
8.6. An Example of Semaphore Settings .................................................................... 20
9. Setting File Handles 23
10. Adjusting Network Settings 25
10.1. Changing Network Adapter Settings .................................................................. 25
10.2. Changing Network Kernel Settings .................................................................... 25
10.3. Flow Control for e1000 Network Interface Cards ................................................. 26
11. Setting Shell Limits for the Oracle User 27
11.1. Limiting Maximum Number of Open File Descriptors for the Oracle User ............... 27
11.2. Limiting Maximum Number of Processes Available for the Oracle User ................. 28
12. Enabling Asynchronous I/O and Direct I/O Support 31
12.1. Relinking Oracle9i R2 to Enable Asynchronous I/O Support ................................. 31
12.2. Relinking Oracle 10g to Enable Asynchronous I/O Support .................................. 32
12.3. Enabling Asynchronous I/O in Oracle 9i and 10g ................................................ 32
12.4. Tuning Asynchronous I/O for Oracle 9i and 10g .................................................. 33
12.5. Verifying Asynchronous I/O Usage ..................................................................... 34
13. Configuring I/O for Raw Partitions 37
13.1. General ............................................................................................................ 37
13.2. Basics of Raw Devices ..................................................................................... 38

Red Hat Enterprise Linux Oracle Tuning Guide
iv
13.3. Using Raw Devices for Oracle Databases .......................................................... 39
13.4. Using Block Devices for Oracle 10g Release 2 in Red Hat Enterprise Linux 4
and 5 ....................................................................................................................... 40
14. Large Memory Optimization, Big Pages, and Huge Pages 41
14.1. Big Pages in Red Hat Enterprise Linux 2.1 and Huge Pages in Red Hat
Enterprise Linux 3 ..................................................................................................... 41
14.2. Usage of Big Pages and Huge Pages in Oracle 9i and 10g ................................. 42
14.3. Sizing Big Pages and Huge Pages .................................................................... 42
14.4. Checking Shared Memory Before Starting Oracle Databases ............................... 42
14.5. Configuring Big Pages in Red Hat Enterprise Linux 2.1 ....................................... 42
14.6. Configuring Huge Pages in Red Hat Enterprise Linux 3 ....................................... 43
14.7. Configuring Huge Pages in Red Hat Enterprise Linux 4 or 5 ................................ 45
14.8. Huge Pages and Shared Memory File System in Red Hat Enterprise Linux 3 ........ 46
15. Growing the Oracle SGA to 2.7 GB in x86 Red Hat Enterprise Linux 2.1 Without
VLM 49
15.1. General ............................................................................................................ 49
15.2. Linux Memory Layout ....................................................................................... 49
15.3. Increasing Space for the SGA in Red Hat Enterprise Linux 2.1 ............................ 50
15.4. Lowering the Mapped Base Address for Shared Libraries in Red Hat Enterprise
Linux 2.1 .................................................................................................................. 51
15.5. Lowering the SGA Attach Address for Shared Memory Segments in Oracle 9i ....... 51
15.6. Allowing the Oracle User to Change the Mapped Base Address for Shared
Libraries .................................................................................................................... 52
16. Growing the Oracle SGA to 2.7/3.42 GB in x86 Red Hat Enterprise Linux 3, 4 and
5 Without VLM 55
16.1. General ............................................................................................................ 55
16.2. Mapped Base Address for Shared Libraries in Red Hat Enterprise Linux 3, 4 and
5 .............................................................................................................................. 55
16.3. Oracle 10g SGA Sizes in Red Hat Enterprise Linux 3, 4 or 5 ............................... 56
16.4. Lowering the SGA Attach Address in Oracle 10g ................................................ 57
17. Using Very Large Memory (VLM) 59
17.1. General ............................................................................................................ 59
17.2. Configuring Very Large Memory (VLM) .............................................................. 60
II. Installing the Oracle Database 10g on Red Hat Enterprise Linux 63
18. Downloading and Unpacking Oracle 10g Installation Files 65
19. Pre-Installation Preparation and Verification 67
19.1. Verifying Memory and Swap Space ................................................................... 67
19.2. Verifying Temporary(/tmp) Space ...................................................................... 67
19.3. Verifying Software Packages (RPMs) ................................................................. 67
19.4. Verifying Kernel Parameters .............................................................................. 71
20. Installing Required Software Packages 75
20.1. 10g R2 on Red Hat Enterprise Linux 4 and 5 x86-64 version ............................... 75
20.2. 10g R2 on Red Hat Enterprise Linux 4 and 5 (x86) ............................................. 77
20.3. 10g R1 on Red Hat Enterprise Linux 4 and 5 (x86-64) ........................................ 78
20.4. 10g R1 on Red Hat Enterprise Linux 4 and 5 (x86) ............................................. 78
20.5. Oracle 10g R1 and R2 on Red Hat Enterprise Linux 3 (x86) ................................ 79
20.6. Oracle 10g R1 on Red Hat Enterprise Linux 3 (x86_64) ...................................... 79

v
20.7. Oracle 10g R1 on Red Hat Enterprise Linux 2.1 (x86) ......................................... 80
20.8. Verifying and Updating the redhat-release File .................................................... 80
21. Sizing Disk Space for Oracle 10g 83
22. Setting Shell Limits for Your Oracle User 85
23. Creating Oracle User Accounts 87
24. Creating Oracle Directories 89
24.1. Optimal Flexible Architecture (OFA) for 10g R1 (10.1.0.2) .................................... 89
25. Setting Oracle Environments 91
26. Installing Oracle Database 10g 93
26.1. Installing Oracle 10g on a Remote Linux Server ................................................. 93
26.2. Installing Oracle 10gR2 Cluster Ready Services (CRS) with MPIO ....................... 93
26.3. Starting Oracle Universal Installer ...................................................................... 97
26.4. Using Oracle Universal Installer (OUI) ................................................................ 98
26.5. Updating after the Oracle Universal Installer ..................................................... 100
27. Oracle Post Installation Tasks 103
27.1. Startup and Shutdown of the Oracle 10g Database ........................................... 103
27.2. Shutdown of other Oracle 10g Background Processes ...................................... 103
28. Tips and Hints for Oracle 10g on Red Hat Enterprise Linux 105
29. Oracle 10g and Linux Installation Errors and Troubleshooting 107
III. Installing the Oracle9i 32 bit Database on Red Hat Enterprise Linux 115
30. Preparing Red Hat Enterprise Linux for an Oracle Database Installation 117
30.1. Unpacking and Downloading the Oracle9i Installation Files ................................ 117
30.2. Setting Swap Space ....................................................................................... 117
30.3. Setting Shared Memory .................................................................................. 118
30.4. Examining Temporary(/tmp) Space .................................................................. 118
30.5. Sizing Oracle Disk Space ................................................................................ 118
31. Verifying Required Packages(RPMs) 119
31.1. Required Packages for Red Hat Advanced Server 2.1 ....................................... 119
31.2. Required Packages for Red Hat Enterprise Linux 3 ........................................... 119
31.3. Required Packages for Red Hat Enterprise Linux 4 ........................................... 120
32. Setting Up a Working Environment for Oracle 123
32.1. Creating Oracle User Accounts ....................................................................... 123
32.2. Creating Oracle Directories ............................................................................. 123
32.3. Setting Oracle Environment Variables .............................................................. 123
33. Starting runInstaller 125
34. Installing Oracle9i R2 (9.2.0.1.0) on Red Hat Advanced Server 2.1 127
35. Installing Oracle9i R2 (9.2.0.4.0) on Red Hat Enterprise Linux 3 129
35.1. Installing Oracle9i R2 (9.2.0.1.0) on Red Hat Enterprise Linux 3 ......................... 129
35.2. Patching Oracle9i to 9.2.0.4.0 on Red Hat Enterprise Linux 3 ............................ 132
35.3. Patching Oracle Intelligent Agent on Red Hat Enterprise Linux 3 ........................ 134
36. Installing Oracle9i R2 (9.2.0.6.0) on Red Hat Enterprise Linux 4 137
36.1. Installing Oracle9i R2 (9.2.0.4.0) on Red Hat Enterprise Linux 4 ......................... 137

Red Hat Enterprise Linux Oracle Tuning Guide
vi
36.2. Patching Oracle9i R2 to 9.2.0.6.0 on Red Hat Enterprise Linux 4 ....................... 138
37. Starting and Shutting down the Oracle9i Database 141
38. Oracle Installation Errors 143
39. Reference List 151
A. Revision History 153

Part I. Tuning and Optimizing
Red Hat Enterprise Linux for
Oracle Database 9i and 10g

Chapter 1.
3
Introduction
This guide covers optimizations for Red Hat Enterprise Linux x86 (32 bit) and x86_64 (64 bit)
platforms running Oracle 9i R2 (32 bit or 64 bit) and Oracle 10g R1/R2 (32 bit or 64 bit) standalone
and RAC databases. This white paper covers Red Hat Enterprise Linux Advanced Server 2.1, 3, 4
and 5. Various workarounds covered in this article are due to the 32 bit address limitations of the x86
platform. However, many steps described in this document also apply to x86-64 platforms. Sections
that do not specifically say that its only applicable to 32bit or 64bit apply to both platforms. If you think
that a section is not very clear on that, let me know.For supported system configurations and limits for
Red Hat Enterprise Linux releases, see http://www.redhat.com/rhel/details/limits/. For instructions on
installing Oracle 10g and 9i databases on Red Hat Enterprise Linux, see Appendix A and Appendix B
respectively.

4

Chapter 2.
5
Hardware Architectures and Linux
Kernels
2.1. General
When it comes to large databases the hybrid x86-64 architecture platform is strongly recommended
over the 32 bit x86 platform. 64 bit platforms can access more than 4GB of memory without
workarounds. With 32 bit platforms there are several issues that require workaround solutions for
databases that use lots of memory, for example refer to Chapter 17, Using Very Large Memory
(VLM). If you are not sure whether you are on a 32 bit or 64 bit hardware, run dmidecode or cat /
proc/cpuinfo. Running uname -a can be misleading since 32 bit Linux kernels can run on x86-64
platforms. But if uname -a displays x86-64, then you are running a 64 bit Linux kernel on a x86_64
platform.
2.2. 32 bit Architecture and the hugemem Kernel
In Red Hat Enterprise Linux 3, 4 or 5 the smp kernel can be used on systems with up to 16 GB of
RAM. The hugemem kernel is required in order to use all the memory on systems that have more
than 16GB of RAM up to 64GB. However, it is recommend to use the hugemem kernel even on
systems that have 8GB of RAM or more due to the potential issue of "low memory" starvation (see
next section) that can happen on database systems with 8 GB of RAM. The stability you get with
the hugemem kernel on larger systems outperforms the performance overhead of address space
switching.
With x86 architecture the first 16MB-896MB of physical memory is known as "low
memory" (ZONE_NORMAL) which is permanently mapped into kernel space. Many kernel resources
must live in the low memory zone. In fact, many kernel operations can only take place in this zone.
This means that the low memory area is the most performance critical zone. For example, if you run
resource-intensive applications or have a lot of memory installed and are simultaneously running
resource-intensive applications, memory addresses below 896MB can become constrained. This
happens because more kernel structures must be allocated to these low memory addresses. Low
memory starvation happens when LowFree in /proc/meminfo becomes very low accompanied
by a sudden spike in paging activity. To free up memory in the low memory zone, the kernel bounces
buffers aggressively between low memory and high memory which becomes noticeable as paging (do
not confuse it with paging to the swap partition). If the kernel is unable to free up enough memory in
the low memory zone, then the kernel can hang the system.
Paging activity can be monitored using the vmstat command or using the sar command (option '-
B') which comes with the sysstat RPM. Since Linux tries to utilize the whole low memory zone, a
low LowFree in /proc/meminfo does not necessarily mean that the system is out of low memory.
However, when the system shows increased paging activity when LowFree gets below 50MB, then
the hugemem kernel should be installed. The stability you gain from using the hugemem kernel makes
up for any performance impact resulting from the 4GB-4GB kernel/user memory split in this kernel (a
classic 32 bit x86 system splits the available 4 GB address space into 3 GB virtual memory space for
user processes and a 1 GB space for the kernel). To see some allocations in the low memory zone,
refer to /proc/meminfo and slabtop(1) for more information. Note that Huge Pages would free up
memory in the low memory zone since the system has less bookkeeping to do for that part of virtual
memory, see Chapter 17, Using Very Large Memory (VLM).

Chapter 2. Hardware Architectures and Linux Kernels
6
If you install the Red Hat Enterprise Linux 3, 4 or 5 hugemem kernel ensure that any proprietary
drivers you are using (e.g. proprietary multipath drivers) are certified with the hugemem kernel.
In Red Hat Enterprise Linux 2.1, the smp kernel is capable of handling up to 4GB of RAM. The
kernel-enterprise kernel should be used for systems with more than 4GB of RAM up to 16GB.
In Red Hat Enterprise Linux 5, a 32 bit kernel is always a hugemem kernel so there is no need to
install a special kernel.
2.3. The 64 bit Architecture
This is the architecture that should be used whenever possible. If you can go with a x86_64 platform
ensure that all drivers you need are supported on x86_64 (for example proprietary multipath drivers)
Furthermore, ensure that all the required applications are supported on x86_64 as well.

Chapter 3.
7
Kernel Upgrades
Make sure to install the latest kernel where all proprietary drivers, if applicable, are certified and
supported. Note that proprietary drivers are often installed under /lib/modules/<kernel-
version>/kernel/drivers/addon. For example, the EMC PowerPath drivers can be found in
the following directory when running the 2.4.21-32.0.1.ELhugemem kernel:
$ ls -al /lib/modules/2.4.21-32.0.1.ELhugemem/kernel/drivers/addon/emcpower
total 732
drwxr-xr-x 2 root root 4096 Aug 20 13:50 .
drwxr-xr-x 19 root root 4096 Aug 20 13:50 ..
-rw-r--r-- 1 root root 14179 Aug 20 13:50 emcphr.o
-rw-r--r-- 1 root root 2033 Aug 20 13:50 emcpioc.o
-rw-r--r-- 1 root root 91909 Aug 20 13:50 emcpmpaa.o
-rw-r--r-- 1 root root 131283 Aug 20 13:50 emcpmpap.o
-rw-r--r-- 1 root root 113922 Aug 20 13:50 emcpmpc.o
-rw-r--r-- 1 root root 75380 Aug 20 13:50 emcpmp.o
-rw-r--r-- 1 root root 263243 Aug 20 13:50 emcp.o
-rw-r--r-- 1 root root 8294 Aug 20 13:50 emcpsf.o
$
Therefore, when you upgrade the kernel you must ensure that all proprietary modules can be found
in the right directory so that the kernel can load them. To check which kernels are installed, run the
following command:
$ rpm -qa | grep kernel
To check which kernel is currently running, execute the following command:
$ uname -r
For example, to install the 2.4.21-32.0.1.ELhugemem kernel, download the kernel-hugemem RPM and
execute the following command:
# rpm -ivh kernel-hugemem-2.4.21-32.0.1.EL.i686.rpm
Note
Never upgrade the kernel using the RPM option '-U'. The previous kernel should always
be available if the newer kernel does not boot or work properly.
To make sure the right kernel is booted, check the /etc/grub.conf file if you use GRUB and
change the "default" attribute if necessary. Here is an example:
default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
title Red Hat Enterprise Linux AS (2.4.21-32.0.1.ELhugemem)
root (hd0,0)
kernel /vmlinuz-2.4.21-32.0.1.ELhugemem ro root=/dev/sda2
initrd /initrd-2.4.21-32.0.1.ELhugemem.img
title Red Hat Enterprise Linux AS (2.4.21-32.0.1.ELsmp)
root (hd0,0)
kernel /vmlinuz-2.4.21-32.0.1.ELsmp ro root=/dev/sda2

Chapter 3. Kernel Upgrades
8
initrd /initrd-2.4.21-32.0.1.ELsmp.img
In this example, the "default" attribute is set to "0" which means that the
2.4.21-32.0.1.ELhugemem kernel will be booted. If the "default" attribute would be set to
"1", then 2.4.21-32.0.1.ELsmp would be booted. After you installed the newer kernel reboot the
system. Once you are sure that you do not need the old kernel anymore, you can remove the old
kernel by running:
# rpm -e <OldKernelVersion>
When you remove a kernel, you do not need to update /etc/grub.conf.

Chapter 4.
9
Kernel Boot Parameters
4.1. General
The Linux kernel accepts boot parameters when the kernel is started. Very often it is used to provide
information to the kernel about hardware parameters where the kernel would have problems or to
overwrite default values. Red Hat Enterprise Linux 3 uses 2.4 based kernels, Red Hat Enterprise Linux
4 and 5 use 2.6 based kernels.
For a list of kernel parameters in Red Hat Enterprise Linux 4 and 5, see /usr/share/doc/
kernel-doc-2.6.9/Documentation/kernel-parameters.txt. This file does not exist if
the kernel-doc RPM is not installed. And for a list of kernel parameters in Red Hat Enterprise
Linux3 and Red Hat Enterprise Linux 2.1, see /usr/src/linux-2.4/Documentation/kernel-
parameters.txt which comes with the kernel-doc RPM.
4.2. The I/O Scheduler
Starting with the 2.6 kernel, for example Red Hat Enterprise Linux 4 or 5, the I/O scheduler can be
changed at boot time which controls the way the kernel commits reads and writes to disks. For more
information on various I/O scheduler, see Choosing an I/O Scheduler for Red Hat Enterprise Linux 4
and the 2.6 Kernel 1. Red Hat Enterprise Linux 5 allows users to change I/O schedulers dynamically,
one way this can be done is by executing the command echo sched_name > /sys/block/
<sdx>/queue/scheduler.
The Completely Fair Queuing (CFQ) scheduler is the default algorithm in Red Hat Enterprise Linux
4 which is suitable for a wide variety of applications and provides a good compromise between
throughput and latency. In comparison to the CFQ algorithm, the Deadline scheduler caps maximum
latency per request and maintains a good disk throughput which is best for disk-intensive database
applications. Hence, the Deadline scheduler is recommended for database systems. Also, at the time
of this writing there is a bug in the CFQ scheduler which affects heavy I/O, see Metalink Bug:5041764.
Even though this bug report talks about OCFS2 testing, this bug can also happen during heavy IO
access to raw or block devices and as a consequence could evict RAC nodes.
To switch to the Deadline scheduler, the boot parameter elevator=deadline must be passed to the
kernel that is being used. Edit the /etc/grub.conf file and add the following parameter to the kernel
that is being used, in this example 2.4.21-32.0.1.ELhugemem:
title Red Hat Enterprise Linux Server (2.6.18-8.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-8.el5 ro root=/dev/sda2 elevator=deadline
initrd /initrd-2.6.18-8.el5.img
This entry tells the 2.6.18-8.el5 kernel to use the Deadline scheduler. Make sure to reboot the
system to activate the new scheduler.
1 http://www.redhat.com/magazine/008jun05/features/schedulers/

10

Chapter 5.
11
Memory Usage and Page Cache
5.1. Checking the Memory Usage
To determine the size and usage of memory, you can enter the following command:
grep MemTotal /proc/meminfo
You can find a detailed description of the entries in /proc/meminfo at http://www.redhat.com/advice/
tips/meminfo.html.
Alternatively, you can use the free(1) command to check the memory:
$ free
total used free shared buffers cached
Mem: 4040360 4012200 28160 0 176628 3571348
-/+ buffers/cache: 264224 3776136
Swap: 4200956 12184 4188772
$
In this example the total amount of available memory is 4040360 KB. 264224 KB are used by
processes and 3776136 KB are free for other applications. Do not get confused by the first line which
shows that 28160KB are free! If you look at the usage figures you can see that most of the memory
use is for buffers and cache. Linux always tries to use RAM to speed up disk operations by using
available memory for buffers (file system metadata) and cache (pages with actual contents of files
or block devices). This helps the system to run faster because disk information is already in memory
which saves I/O operations. If space is needed by programs or applications like Oracle, then Linux will
free up the buffers and cache to yield memory for the applications. If your system runs for a while you
will usually see a small number under the field "free" on the first line.
5.2. Tuning the Page Cache
Page Cache is a disk cache which holds data of files and executable programs, for example pages
with actual contents of files or block devices. Page Cache (disk cache) is used to reduce the number
of disk reads. To control the percentage of total memory used for page cache in Red Hat Enterprise
Linux 3, the following kernel parameter can be changed:
# cat /proc/sys/vm/pagecache
1 15 30
The above three values are usually good for database systems. It is not recommended to set the
third value very high, around 100, as it used to be with older Red Hat Enterprise Linux 3 kernels. This
can cause significant performance problems for database systems. If you upgrade to a newer kernel
like 2.4.21-37, then these values will automatically change to "1 15 30" unless its set to different
values in /etc/sysctl.conf. For information on tuning the pagecache kernel parameter, see
Understanding Virtual Memory. Note this kernel parameter does not exist in Red Hat Enterprise Linux
4.
The pagecache parameters can be changed in the proc file system without reboot:
# echo "1 15 30" > /proc/sys/vm/pagecache

Chapter 5. Memory Usage and Page Cache
12
Alternatively, you can use sysctl(8) to change it:
# sysctl -w vm.pagecache="1 15 30"
To make the change permanent, add the following line to the file /etc/sysctl.conf. This file is
used during the boot process.
# echo "vm.pagecache=1 15 30" >> /etc/sysctl.conf
With Red Hat Enterprise Linux 4 and 5, the pagecache is dynamically adjusted. You can adjust the
minimum free pages using the following command:
# echo 1024 > /proc/sys/vm/min_free_kbytes
To make the change permanent, add the following line to the file /etc/sysctl.conf:
# echo vm.min_free_kbytes=1024 >> /etc/sysctl.conf
The pagecache pages can be reclaimed by adjusting the swappiness percentage as described in
the next section.

Chapter 6.
13
Swap Space
6.1. General
In some cases it is good for the swap partition to be used. For example, long running processes often
access only a subset of the page frames they obtained. This means that the swap partition can safely
be used even if memory is available because system memory could be better served for disk cache to
improve overall system performance. In fact, in the 2.6 kernel used in Red Hat Enterprise Linux 4 and
5, you can define a threshold when processes should be swapped out in favor of I/O caching. This can
be tuned with the /proc/sys/vm/swappiness kernel parameter. The default value of /proc/sys/
vm/swappiness is 60 which means that applications and programs that have not done a lot lately
can be swapped out. Higher values will provide more I/O cache and lower values will wait longer to
swap out idle applications. Swappiness percentage may be tuned using:
# echo 10 > /proc/sys/vm/swappiness
or,
# echo vm.swappiness=10 >> /etc/sysctl.conf
Depending on your system profile you may see that swap usage slowly increases with the time the
system is up. To display swap usage you can run the free(1) command or you can check the /
proc/meminfo file. When the system uses swap space it will sometimes not decrease afterward.
This saves I/O if memory is needed and pages do not have to be swapped out again when the pages
are already in the swap space. However, if swap usage gets close to 80% - 100% (your threshold may
be lower if you use a large swap space), then a closer look should be taken at the system, see also
Section 6.2, “Checking Swap Space Size and Usage”. Depending on the size of your swap space,
you may want to check swap activity with vmstat or sar if swap allocation is lower than 80%. But
these numbers really depend on the size of the swap space. The vmstat or sar command output the
number of pages swapped. This output field is an important metric. This number should be low or zero
as constant page swapping should be avoided at all costs.
Note
Never add a permanent swap file to the system due to the performance impact on the file
system layer.
Swap Size Recommendations According to Oracle9i Installation Guide Release 2 a minimum of
512MB of RAM is required to install Oracle9i Server. According to Oracle Database Installation Guide
10g Release 2 at least 1024MB of RAM is required for 10g R2.
For 10g R2, Oracle gives the following swap space requirement:
RAM Swap Space
1 GB - 2 GB 1.5 times the size of RAM
2 GB - 8 GB Equal to the size of RAM
Greater than 8GB 0.75 times the size of RAM
Table 6.1. Recommended Swap Space Requirements for 10g R2

Chapter 6. Swap Space
14
6.2. Checking Swap Space Size and Usage
You can check the size and current usage of swap space by running the command: grep
SwapTotal /proc/meminfo
Swap usage may slowly increase as shown above but should stop at some point. If swap usage
continues to grow steadily or is already large, then one of the following choices may need to be
considered:
• Adding more RAM.
• Reducing the size of the SGA.
• Increasing the size of the swap space.
If you see constant swapping, then you need to either add more RAM or reduce the size of the SGA.
Constant swapping should be avoided at all cost. You can check current swap activity using the
following commands:
$ vmstat 3 100
procs memory swap io system cpu
r b swpd free buff cache si so bi bo in cs us sy id wa
1 0 0 972488 7148 20848 0 0 856 6 138 53 0 0 99 0
0 1 0 962204 9388 20848 0 0 747 0 4389 8859 23 24 11 41
0 1 0 959500 10728 20848 0 0 440 313 1496 2345 4 7 0 89
0 1 0 956912 12216 20848 0 0 496 0 2294 4224 10 13 0 77
1 1 0 951600 15228 20848 0 0 997 264 2241 3945 6 13 0 81
0 1 0 947860 17188 20848 0 0 647 280 2386 3985 9 9 1 80
0 1 0 944932 19304 20848 0 0 705 0 1501 2580 4 9 0 87
The fields si and so show the amount of memory paged in from disk and paged out to disk,
respectively. If the server shows continuous swap activity then more memory should be added or the
SGA size should be reduced. To check the history of swap activity, you can use the sar command. For
example, to check swap activity from Oct 12th:
# ls -al /var/log/sa | grep "Oct 12"
-rw-r--r-- 1 root root 2333308 Oct 12 23:55 sa12
-rw-r--r-- 1 root root 4354749 Oct 12 23:53 sar12
# sar -W -f /var/log/sa/sa12
Linux 2.4.21-32.0.1.ELhugemem (rac01prd) 10/12/2005
12:00:00 AM pswpin/s pswpout/s
12:05:00 AM 0.00 0.00
12:10:00 AM 0.00 0.00
12:15:00 AM 0.00 0.00
12:20:00 AM 0.00 0.00
12:25:00 AM 0.00 0.00
12:30:00 AM 0.00 0.00
...
The fields pswpin and pswpout show the total number of pages brought in and out per second,
respectively.
If the server shows sporadic swap activity or swap activity for a short period time at certain intervals,
then you can either add more swap space or RAM. If swap usage is already very large, do not confuse
very large swap usage with constant swapping, then more RAM is recommended.