近期，一套Oracle 22.214.171.124数据库进行了存储迁移，期间重建了数据库的文件系统，之后发现log files sync等待事件平均耗时增加了一倍，应用队列有明显的阻塞。
Db_block_size Requirements For Direct IO / Concurrent IO (Doc ID 418714.1)
In this Document
Oracle Database - Enterprise Edition - Version 126.96.36.199 to 188.8.131.52 [Release 9.2 to 11.2]
IBM AIX on POWER Systems (64-bit)
***Checked for relevance on 20-Jan-2012***
Running benchmarks with Direct IO and Concurrent IO.
disk_asynch_io is set to true, filesystemio_options = setall and db_block_size=8k
Will DIO and CIO be used when the operating system uses 4k blocks and Oracle is set to 8k blocks or is it required to set the db_block_size to 4k so it matches exactly what the OS has?
The following is extracted from IBM paper- Oracle Architecture and Tuning on AIX.
Please refer to
(c) 2011 International Business Machines, Inc. - IBM Americas Advanced Technical Support
Oracle Architecture and Tuning on AIX
Date : 21 September 2011
Section: 2.3.8. JFS2 file system DIO/CIO mount options, p.54
For applications such as Oracle Database that provide their own I/O serialization mechanisms, JFS2 (beginning with AIX 5.2.10) offers the Concurrent I/O (CIO) option. Under Concurrent I/O, multiple threads may simultaneously perform reads and writes on a shared file. Applications that do not enforce serialization for accesses to shared files (including operating system level utilities) should not use Concurrent I/O, as this could result in data corruption due to competing accesses and /or severe performance penalties.
Concurrent I/O should only be used for Oracle .dbf files (data & index, rbs or undo, system and temp). When used for online redo logs or control files, these files should be isolated in their own JFS2 filesystem(s) that have been created with agblksize=512.
Filesystem containing .dbf files should be created with agblksize=2048 if DB_BLOCK_SIZE=2k, or agblksize=4096 if DB_BLOCK_SIZE>= 4k. Failure to implement these agblksize guidelines is likely to result in a severe performance penalty.
Do not under any circumstances, use CIO mount option for the filesystem containing the Oracle binaries. Additionally, do not use DIO/CIO options for filesystem containing archive logs or any other files not already discussed.
The following command can be used to query agblksize (needs to be run as root):
% lsfs -q <filesystem_name>
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