Red Hat ENTERPRISE LINUX AS 2.1 - Installationsanleitung PDF herunterladen (Seite 40)

Chapter 12. Enabling Asynchronous I/O and Direct I/O Support

# echo 1048576 > /proc/sys/fs/aio-max-size

Alternatively, you can use sysctl(8) to change it:

# sysctl -w fs.aio-max-size=1048576

To make the change permanent, add the following line to the /etc/sysctl.conf file. This file is

used during the boot process:

$ echo "fs.aio-max-size=1048576" >> /etc/sysctl.conf

12.5. Verifying Asynchronous I/O Usage

To verify whether $ORACLE_HOME/bin/oracle was linked with asynchronous I/O, you can use the

Linux commands ldd and nm.

In the following example, $ORACLE_HOME/bin/oracle was relinked with asynchronous I/O:

$ ldd $ORACLE_HOME/bin/oracle | grep libaio

libaio.so.1 => /usr/lib/libaio.so.1 (0x0093d000)

$ nm $ORACLE_HOME/bin/oracle | grep io_getevent

w io_getevents@@LIBAIO_0.1

In the following example, $ORACLE_HOME/bin/oracle has NOT been relinked with asynchronous I/

$ ldd $ORACLE_HOME/bin/oracle | grep libaio

$ nm $ORACLE_HOME/bin/oracle | grep io_getevent

w io_getevents

If $ORACLE_HOME/bin/oracle is relinked with asynchronous I/O it does not necessarily mean that

Oracle is really using it. You also have to ensure that Oracle is configured to use asynchronous I/O

calls, see Enabling Asynchronous I/O Support.

To verify whether Oracle is making asynchronous I/O calls, you can take a look at the /proc/

slabinfo file assuming there are no other applications performing asynchronous I/O calls on the

system. This file shows kernel slab cache information in real time.

On a Red Hat Enterprise Linux 3 system where Oracle does not make asynchronous I/O calls, the

output looks like this:

$ egrep "kioctx|kiocb" /proc/slabinfo

kioctx 0 0 128 0 0 1 : 1008 252

kiocb 0 0 128 0 0 1 : 1008 252

Once Oracle makes asynchronous I/O calls, the output on a Red Hat Enterprise Linux 3 system will

look like this:

$ egrep "kioctx|kiocb" /proc/slabinfo

kioctx 690 690 128 23 23 1 : 1008 252

kiocb 58446 65160 128 1971 2172 1 : 1008 252

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Red Hat ENTERPRISE LINUX AS 2.1 - Installationsanleitung Seite 40