Installation guide

database and each combination of database instances running on the same system are unique. The following
settings proved useful for many Oracle database users and improved the stability and performance of Oracle
servers on Red Hat Enterprise Linux 5. They should be considered as a starting point for the follow-up perfor-
mance tuning.
Ensure the following settings are present in /etc/sysctl.conf:
vm.swappiness=0
vm.dirty_background_ratio=3
vm.dirty_ratio=15
vm.dirty_expire_centisecs=500
vm.dirty_writeback_centisecs=100
Swap Space
General
There are cases where utilizing the swap partition is beneficial. For example, long running processes often ac-
cess 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 (Red Hat Enterprise Linux 4 and later) you can define a threshold where
processes should be swapped out in favor of I/O caching. This can be tuned using the /proc/sys/vm/swap-
piness kernel parameter.
Depending on the system profile ,you may observe swap usage slowly increases with system uptime. To display
swap usage, use the free(1) command or 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, as swap usage approaches 80% -
100% (your threshold may be lower if you use a large swap space), a closer examination of system performance
is recommended, see also Checking Swap Space Size and Usage. Depending on the size of the swap space, you
may want to check swap activity using vmstat or sar if swap allocation is lower than 80%. However, these
numbers depend on the size of the swap space. The actual numbers of swapped pages per time frame from vm-
stat or sar are the important numbers. Constant swapping should be avoided .
Note, never add a permanent swap file to the system due to the performance impact of the file system layer.
Swap Size Recommendations
According to Oracle Database Installation Guide 10g Release 2 at least 1024MB of RAM is required for 10g
R2. Oracle provides generic recommendations regarding the size of swap in MetaLink Note 169706.1. These
recommendations may lead to creation of very large swap space on systems with large amount of memory. The
very large swap may cause sever system performance degradation and can be resolved by reducing swap space.
Red Hat does not recommend allocating greater than 4GB for swap on Red Hat Enterprise Linux 5.
The following table summarizes the swap size recommendations for Oracle 10g R2 on Red Hat Enterprise
Linux 5:
12 | www.redhat.com