DB_FILE_MULTIBLOCK_READ_COUNT Parameter in Oracle

DB_FILE_MULTIBLOCK_READ_COUNT Parameter
DB_FILE_MULTIBLOCK_READ_COUNT parameter is used to specifies the maximum number of blocks read in one I/O operation during a sequential scan. If you want to scan a table, I/O has lot of dependence on the value of this parameter.
The value is mostly dependent on the Operating system.
Default value depend upon maximum I/O Size can be performed by I/O operations.

It is used to control I/O operation like fetch the number of blocks from disk to buffer cache.This parameter basically tell how many block retrieve in single I/O operations. During installation, Oracle is automatically choose the optimal value of this parameter depending on the Operating system.

Check the value of parameter

SQL> Show parameter DB_FILE_MULTIBLOCK_READ_COUNT

NAME                          TYPE    VALUE
----------------------------- ------- -----
db_file_multiblock_read_count integer 37

Change value at session or system level

-- Session Level
SQL> alter session set DB_FILE_MULTIBLOCK_READ_COUNT=128;
Session altered.

-- SYSTEM level
SQL> alter system set DB_FILE_MULTIBLOCK_READ_COUNT=128 scope=both;
System altered.