Ideally, this parameter is the same as or a multiple of the operating system block size for I/O
efficiency.
Before Oracle9i, you might specify a smaller block size (4KB or 8KB) for OLTP systems and
a larger block size (up to 32KB) for DSS (decision support system) databases. However, now that
tablespaces with up to five block sizes can coexist in the same database, a smaller value for DB_
BLOCK_SIZE is fine. However, 8KB is probably preferable as a minimum for any database, unless
it has been rigorously proven in the target environment that a 4KB block size will not cause
performance issues.
SGA_TARGET
Another way that Oracle 10g can facilitate a ???set it and forget it??? database is by the ability to
specify a total amount of memory for all SGA components. If SGA_TARGET is specified, the
parameters DB_CACHE_SIZE, SHARED_POOL_SIZE, LARGE_POOL_SIZE, STREAMS_POOL_
SIZE, and JAVA_POOL_SIZE are automatically sized by Automatic Shared Memory Management
(ASMM). If any of these four parameters are manually sized when SGA_TARGET is also set,
ASMM uses the manually sized parameters as minimums.
Once the instance starts, the automatically sized parameters can by dynamically increased or
decreased, as long as the parameter SGA_MAX_SIZE is not exceeded. The parameter SGA_MAX_
SIZE specifies a hard upper limit for the entire SGA, and it cannot be exceeded or changed until
the instance is restarted.
Regardless of how the SGA is sized, be sure that enough free physical memory is available in
the server to hold the components of the SGA and all background processes; otherwise, excessive
paging will occur and performance will suffer.
Pages:
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135