DB_BLOCK_SIZE Initialization Parameter (92)

The most commonly used block size should be picked as the standard block size. In
many cases, this is the only block size that you need to specify. Typically,
DB_BLOCK_SIZE is set to either 4K or 8K. If you do not set a value for this parameter,
the default data block size is operating system specific, which is generally adequate.

You cannot change the block size after database creation except by re-creating the
database. If the database block size is different from the operating system block size,
ensure that the database block size is a multiple of the operating system block size. For
example, if your operating system block size is 2K (2048 bytes), the following setting
for the DB_BLOCK_SIZE initialization parameter is valid:

DB_BLOCK_SIZE=4096

A larger data block size provides greater efficiency in disk and memory I/O (access
and storage of data). Therefore, consider specifying a block size larger than your
operating system block size if the following conditions exist:
■ Oracle Database is on a large computer system with a large amount of memory
and fast disk drives. For example, databases controlled by mainframe computers
with vast hardware resources typically use a data block size of 4K or greater.
■ The operating system that runs Oracle Database uses a small operating system
block size. For example, if the operating system block size is 1K and the default
data block size matches this, the database may be performing an excessive amount
of disk I/O during normal operation. For best performance in this case, a database
block should consist of multiple operating system blocks.

DB_BLOCK_SIZE引數
1. 只能為4K或8K , 與作業系統相關
2. 如果該值與作業系統塊大小不一致 ,需保證該引數值為後者的整倍數
3. 大的快值提供了磁碟I/O與記憶體的效率
4. 如果以下條件存在 ,可考慮使用較大的塊值:
a. 快的磁碟驅動器 , 大的記憶體機器上
b. 執行資料庫的伺服器作業系統使用較小的塊值 ,如1K

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