Adding more buffers in Oracle

Adding memory to the buffers will decrease the available pool of memory in your host for other programs, and this decision should always be given careful consideration. Increasing the size of db_block_size will increase the size of the Oracle SGA. The values of db_block_size are multiplied by the value of db_block_buffers to determine the total amount of memory to allocate for Oracle's I/O buffers.
In general, db_block_size should never be set to less than 8K, regardless of the type of application. Even online transaction processing systems (OLTP) will benefit from using 8K blocks, while systems that perform many full-table scans will benefit from even larger block sizes. Depending on the operating system, Oracle can support up to 16K block sizes. Systems that perform full-table scans can benefit from this approach.

DB_BLOCK_SIZE specifies (in bytes) the size of Oracle database blocks. Typical values are 4096 and 8192. The value of this parameter must be a multiple of the physical block size at the device level. The value for DB_BLOCK_SIZE in effect at the time you create the database determines the size of the blocks. The value must remain set to its initial value.
For Real Application Clusters, this parameter affects the maximum value of the FREELISTS storage parameter for tables and indexes. Oracle uses one database block for each freelist group. Decision support system (DSS) and data warehouse database environments tend to benefit from larger block size values.