Oracle在Linux下使用非同步IO（aio）配置(轉)

1、首先用root使用者安裝以下必要的rpm包

# rpm -Uvh libaio-0.3.106-3.2.x86_64.rpm
# rpm -Uvh libaio-devel-0.3.106-3.2.x86_64.rpm

2、在系統級支援非同步I/O
　　與[Note 225751.1]介紹的在RHEL3裡面設定非同步IO不同，不需要設定aio-max-size，而且'/proc/sys/fs'路徑下也沒有這個檔案。因為從2.6 kernel開始，已經取消了對IO size的限制[Note 549075.1]。另外根據[Note 471846.1]，建議將aio-max-nr的值設定為1048576或更高。

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

3、在資料庫級啟用非同步I/O
　　首先修改資料庫引數。與[Note 225751.1]在RHEL 3裡面設定非同步IO不同，Oracle10gR2預設是開啟了對非同步IO的支援的，不需要重新編譯資料庫軟體。在'$ORACLE_HOME/rdbms/lib'路徑下，也沒有'skgaioi.o'這個檔案。在某些情況下，Oracle無法將IO行為或事件報告給作業系統[Note 365416.1]，因此需要做以下操作。

這裡開始換成oracle使用者

SQL>alter system set disk_asynch_io=TRUE scope=spfile;

SQL>alter system setfilesystemio_options=asynchscope=spfile;

SQL>shutdown immediate
$ cd $ORACLE_HOME/rdbms/lib
$ ln -s /usr/lib/libaio.so.1 skgaio.o
$ make PL_ORALIBS=-laio -f ins_rdbms.mk async_on
SQL>startup

在Oracle10gR2中AIO預設已經是開啟的了。可以透過ldd或者nm來檢查oracle是否已經啟用了AIO支援，有輸出代表已經啟用。

[oraprod@db01 ~]$/usr/bin/ldd $ORACLE_HOME/bin/oracle | grep libaio
libaio.so.1 => /usr/lib64/libaio.so.1 (0x00002aaaac4a9000)
[oraprod@db01 ~]$/usr/bin/nm $ORACLE_HOME/bin/oracle | grep io_getevent
w io_getevents@@LIBAIO_0.4

4、檢查非同步I/O是否在使用
　 　根據[Note 370579.1]，可以透過檢視slabinfo統計資訊檢視作業系統中AIO是否執行，slab是Linux的記憶體分配器，AIO相關的記憶體結構已經分配，kiocb值的第二列和第三列非0即是已使用。與kernel 2.4.x不同，沒有顯示kiobuf，因為從kernel 2.5.43開始，kiobuf已經從核心中被移除。

$cat /proc/slabinfo | grep kio
kioctx 64 110 384 10 1 : tunables 54 27 8 : slabdata 11 11 0
kiocb 13 315 256 15 1 : tunables 120 60 8 : slabdata 21 21 44

我的實驗過程：
[@localhost ~]$ sqlplus /nolog
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Dec 17 10:37:10 2010
Copyright (c) 1982, 2005, Oracle.All rights reserved.

[oracle@localhost ~]$ /usr/bin/nm $ORACLE_HOME/bin/oracle | grep io_getevent
w io_getevents@@LIBAIO_0.4
[oracle@localhost ~]$
[oracle@localhost ~]$
[oracle@localhost ~]$ /usr/bin/ldd $ORACLE_HOME/bin/oracle | grep libaio
libaio.so.1 => /usr/lib/libaio.so.1 (0x00507000)
[oracle@localhost ~]$ cat /proc/slabinfo | grep kio
kioctx1415256151 : tunables120600 : slabdata110
kiocb00128311 : tunables120600 : slabdata000
## 沒有啟用：
SQL> show parameter disk_asynch_io

NAMETYPE
------------------------------------ ----------------------
VALUE
------------------------------
disk_asynch_ioboolean
TRUE

SQL> sho parameter filesystemio_options

NAMETYPE
------------------------------------ ----------------------
VALUE
------------------------------
filesystemio_optionsstring
none
SQL>
SQL>
SQL> alter system set filesystemio_options = setallscope=both;
alter system set filesystemio_options = setallscope=both
*
ERROR at line 1:
ORA-02095: specified initialization parameter cannot be modified

SQL>
SQL>alter system set filesystemio_options = setallscope=spfile;

System altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area285212672 bytes
Fixed Size1218992 bytes
Variable Size88082000 bytes
Database Buffers192937984 bytes
Redo Buffers2973696 bytes
Database mounted.
Database opened.
[root@localhost ~]# cat /proc/slabinfo | grep kio
kioctx1315256151 : tunables120600 : slabdata110
kiocb731128311 : tunables120600 : slabdata110

9.1.1.1Asynchronous I/O
With synchronous I/O, when an I/O request is submitted to the operating system, the writing process blocks until the write is confirmed as complete. It can then continue processing. With asynchronous I/O, processing continues while the I/O request is submitted and processed. Use asynchronous I/O when possible to avoid bottlenecks.

Some platforms support asynchronous I/O by default, others need special configuration, and some only support asynchronous I/O for certain underlying file system types.

9.1.1.2FILESYSTEMIO_OPTIONS Initialization Parameter
You can use theFILESYSTEMIO_OPTIONSinitialization parameter to enable or disable asynchronous I/O or direct I/O on file system files. This parameter is platform-specific and has a default value that is best for a particular platform. It can be dynamically changed to update the default setting.

FILESYTEMIO_OPTIONScan be set to one of the following values:

ASYNCH:enable asynchronous I/O on file system files, which has no timing requirement for transmission.

DIRECTIO:enable direct I/O on file system files, which bypasses the buffer cache.

SETALL:enable both asynchronous and direct I/O on file system files.

NONE:disable both asynchronous and direct I/O on file system files.