Parameters Related to I/O
The parameters that affect I/O are:
These parameters also affect the optimizer, which ensures optimal performance for parallel execution of I/O operations.
Oracle Database Reference for information about initialization parameters
DB_CACHE_SIZE
When you perform parallel update, merge, and delete operations, the buffer cache behavior is very similar to any OLTP system running a high volume of updates.
DB_BLOCK_SIZE
The recommended value for this parameter is 8 KB or 16 KB.
Set the database block size when you create the database. If you are creating a new database, use a large block size such as 8 KB or 16 KB.
DB_FILE_MULTIBLOCK_READ_COUNT
This parameter determines how many database blocks are read with a single operating system READ call. In this release, the default value of this parameter is a value that corresponds to the maximum I/O size that can be performed efficiently. The maximum I/O size value is platform-dependent and is 1 MB for most platforms. If you set DB_FILE_MULTIBLOCK_READ_COUNT to an excessively high value, your operating system lowers the value to the highest allowable level when you start your database.
DISK_ASYNCH_IO and TAPE_ASYNCH_IO
The recommended value for both of these parameters is TRUE.
These parameters enable or disable the operating system's asynchronous I/O facility. They allow query server processes to overlap I/O requests with processing when performing table scans. If the operating system supports asynchronous I/O, leave these parameters at the default value of TRUE. Figure 8-6 illustrates how asynchronous read works.
Asynchronous operations are currently supported for parallel table scans, hash joins, sorts, and serial table scans. However, this feature can require operating system-specific configuration and may not be supported on all platforms.