oracle DB_FILE_MULTIBLOCK_READ_COUNT

oracle 官方文档：http://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams047.htm

Property	Description
Parameter type	Integer
Default value	The default value corresponds to the maximum I/O size that can be efficiently performed and is platform-dependent
Modifiable	ALTER SESSION, ALTER SYSTEM
Range of values	Operating system-dependent
Basic	No

DB_FILE_MULTIBLOCK_READ_COUNT

g

Even though the default value may be a large value, the optimizer will not favor large plans if you do not set this parameter. It would do so only if you explicitly set this parameter to a large value.

Online transaction processing (OLTP) and batch environments typically have values in the range of 4 to 16 for this parameter. DSS and data warehouse environments tend to benefit most from maximizing the value of this parameter. The optimizer is more likely to choose a full table scan over an index if the value of this parameter is high.

DB_BLOCK_SIZE). If you set this parameter to a value greater than the maximum, Oracle uses the maximum.

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE    10.2.0.1.0      Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production

SQL>

SQL> select name,type,value,isdefault from v$parameter where name='db_file_multiblock_read_count';

NAME                                 TYPE VALUE                ISDEFAULT
------------------------------ ---------- -------------------- --------------------
db_file_multiblock_read_count  ########## 16                   FALSE

SQL>