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Tuning for Oracle9i on Linux

Extended Buffer Cache Support

Oracle9i can allocate and use more than 4 GB of memory for the database buffer cache. This section describes the limitations and requirements of the extended buffer cache support on Linux.

See Also: Oracle9i Database Concepts for more information on the extend cache feature.

In-Memory File System

To use the extended buffer cache support on Linux, create an in-memory file system on the /dev/shm mount point equal in size or larger than the amount of memory that you intend to use for the database buffer cache.

For example, for Linux to create an 8 GB shmfs file system on the /dev/shm mount point, enter the following as the root user:

$ mount -t shm shmfs -o size=8g /dev/shm

When Oracle9i starts with the extended buffer cache feature enabled, it creates a file in the /dev/shm directory that corresponds to the Oracle buffer cache.

USE_INDIRECT_DATA_BUFFERS Parameter

To enable the extended buffer cache feature, set the USE_INDIRECT_DATA_BUFFERS parameter to true in the initsid.ora file. Doing this allows Oracle9i to specify a larger buffer cache.

Dynamic Cache Parameters

Do not use the following dynamic cache parameters while the extended cache feature is enabled:

• DB_CACHE_SIZE

• DB_2K_CACHE_SIZE

• DB_4K_CACHE_SIZE

• DB_8K_CACHE_SIZE

• DB_16K_CACHE_SIZE

• DB_32K_CACHE_SIZE

If the extended cache feature is enabled, use the DB_BLOCK_BUFFERS parameter to specify the database cache size.

Limitations

The following limitations apply to the extended buffer cache feature on Linux:

• You cannot change the size of the buffer cache while the instance is running.

• You cannot create or use tablespaces with non-standard block sizes.

See Also: Oracle9i SQL Reference for information on the standard block size used by the CREATE TABLE SPACE command.

Asynchronous I/O Support

Oracle9i supports kernel asynchronous I/O. This feature is disabled by default. If you are running Oracle9i on a system that supports kernel asynchronous I/O and that is certified by Oracle Corporation to use asynchronous I/O, perform the following steps to enable asynchronous I/O support:

1. As the root user, change directory to the $ORACLE_HOME/rdbms/lib directory.

2. Enter the following commands:

   $ make -f ins_rdbms.mk async_on
   
   

   
   

   Note: If you receive the "/usr/bin/ld: cannot find -laio" error, then the system does not support kernel asynchronous I/O and you must enter the following command to restore the Oracle instance to a usable state: $ make -f ins_rdbms.mk async_off

   
   

By default, the DISK_ASYNCH_IO parameter in the initsid.ora file is set to true to enable asynchronous I/O on raw devices. To enable asynchronous I/O on filesystem files:

1. Ensure that all Oracle data files are located on file systems that support asynchronous I/O.

2. Set the FILESYTEMIO_OPTIONS parameter in the initsid.ora file to asynch.