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Donald K. Burleson

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SGA Regions

Now, let's take a quick look at the important regions within the SGA. The most important areas of RAM within the SGA include:

• Data Buffer Caches – These RAM areas define RAM space for incoming data blocks and are governed by the following parameters. The sum of all of these parameter values determines the total space reserved for Oracle data blocks.

• db_cache_size
• db_keep_cache_size)
• db_recycle_cache_size
• db_2k_cache_size
• db_4k_cache_size
• db_8k_cache_size
• db_16k_cache_size
• db_32k_cache_size

• Log Buffer – This is the RAM space for writing redo log files. The log_buffer parameter should never exceed 5 megabytes, and this RAM space is used solely to hold the redo images until the LGWR background process writes the redo log entries into the redo log filesystem.

• Shared Pool - This RAM area is used to process SQL statements (inside a shared pool area called the library cache) and hold control structures for the instance. It is governed by the shared_pool_size parameter.

To re-allocate RAM within Oracle, we use alter system commands to change important Oracle parameters that govern the size of the memory regions within the SGA. Let’s take a close look at these parameters and see how they are used.

The above text is an excerpt from "Creating a Self Tuning Oracle Database", by Rampant TechPress.  It is only $9.95 and all scripts in this tips can be immediately downloaded.


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