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Warning: OS async I/O limit 128 is lower than.. in Alert log

原创 Linux操作系统 作者:thompsun 时间:2011-01-21 17:25:46 0 删除 编辑

1. For more details about how to tune ASYNC I/O for Raw disk partitions on HP_UX kindly refer,

Oracle Database Administrator's Reference
11g Release 1 (11.1) for Linux and UNIX-Based Operating Systems
Part Number B32009-05
Appendix B 'Administering Oracle Database on HP-UX'
section 'Asynchronous Input-Output'

For Oracle 10G,

http://download.oracle.com/docs/cd/B19306_01/server.102/b15658/appb_hpux.htm#i637036

For Oracle 11G,

http://download.oracle.com/docs/cd/B28359_01/server.111/b32009/appb_hpux.htm#i637036


NOTE : The above document can be given as an 'example' of what to check for HP. For other platforms, check the relevant section in the same doc OR refer back to the OS/hardware vendors for further guidance.


2. For File system to improve the performance,

Set disk_asynch_io = FALSE and increase the DB writer process.

Based upon the number of CPUs and the number of processor groups, Oracle either selects an
appropriate default setting for DB_WRITER_PROCESSES or adjusts a user-specified setting.

NOTE : Make sure dbwr_io_slaves set to 0.

Example for 4 CPU machine,

SQL>alter system set dbwr_io_slaves = 0 scope = spfile ;
SQL>alter system set db_writer_processes = 4 scope = spfile ;

Sometime the false Warning message will be displayed in alert log eventhough the DISK_AYNC_IO is set to FALSE.

Inorder to stop this Warning message we have to apply this Patch 8475825 which is available for most of the OS.

Reference Bug 8475825 - OS ASYNC I/O LIMIT 128 IS LOWER THAN RECOVERY BATCH 1024

3.On Redhat Linux 4 and 5 the recommended action is to raise the value of /proc/sys/fs/aio-max-nr.
eg: Set the value to 1048576 or higher.

============================

To set the value forSUSE linux:

In the file /etc/sysctl.conf , add the below entry:
fs.aio-max-nr=1048576

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