The SGA_TARGET Initialization Parameter (74)

The SGA_TARGET initialization parameter reflects the total size of the SGA and
includes memory for the following components:
■ Fixed SGA and other internal allocations needed by the Oracle Database instance
■ The log buffer
■ The shared pool
■ The Java pool
■ The buffer cache
■ The keep and recycle buffer caches (if specified)
■ Nonstandard block size buffer caches (if specified)
■ The Streams pool
It is significant that SGA_TARGET includes the entire memory for the SGA, in contrast
to earlier releases in which memory for the internal and fixed SGA was added to the
sum of the configured SGA memory parameters. Thus, SGA_TARGET gives you precise
control over the size of the shared memory region allocated by the database. If
SGA_TARGET is set to a value greater than SGA_MAX_SIZE at startup, then the latter is
bumped up to accommodate SGA_TARGET.

SGA_TARGET : 指定sga的大小 ， 包含以下元件
1. Oracle資料庫例項需要的internal和固定SGA
2. 重做日誌快取區
3. 共享池 ， java池 ， 快取記憶體等等
最後一句話的意思應該是例項啟動時 ，當SGA_TARGET設定大於SGA_MAX_SIZE ， 稍後
作業系統分配給Oracle記憶體將bumped up(突然增加)來適應SGA_TARGET

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