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Lesson 1

Understanding Oracle's Memory Architecture

Now that you know about files and processes, it is time to learn about the last piece of the architecture puzzle, which is memory.
Oracle uses several memory structures: the
  1. System Global Area,
  2. Program Gobal Areas,
  3. and Sort Areas.
See Figure 1 below

Oracle Database Memory Structures
Figure 1: Oracle Database Memory Structures consisting of 1) Server Processes and 2) Background Process interacting with the System Global Area

Understanding and properly sizing the System Global Area, Program Global Areas, and Sort Areas can have big impact on overall database performance.
The System Global Area is the most significant structure, and the most important to understand. You've already seen, in the previous module, that it's divided into several smaller areas known as the database buffer cache, the redo log buffer, and the shared pool. This module goes into more detail about each of those structures, particularly the shared pool.
When you are done with this module, you should be able to:
  1. Describe the memory structures that make up the SGA
  2. Describe how the database buffer cache manages data blocks
  3. Describe the purpose of the three types of buffer pools
  4. Describe the function of the redo log buffer.
  5. Identify the function of the large pool
  6. Describe how each session gets its own memory
  7. List the contents of the PGA
  8. Describe how Oracle uses memory for sorting
The knowledge that you gain in this lesson will enable you to understand many of the tuning issues that will arise when you manage an Oracle database.