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.

See Also:

Oracle Database Reference for information about initialization parameters


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.


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.


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.


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.

Figure 8-6 Asynchronous Read

Description of Figure 8-6 follows
Description of "Figure 8-6 Asynchronous Read"

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.