1. Outline Introduction to Oracle Memory Structures SGA, PGA, SCA The Specifics of the System Global Area (SGA) Structures Overview of Program Global Areas (PGAs) and Software Code Areas (SCA) Demonstration

2. Oracle Memory Structures in a Nutshell Source: Oracle Database Concepts 10g

3. System Global Area (SGA) Shared Area of Memory for One Instance Data and Control Information Collection of Structures Buffer Cache, Java Pool, Shared Pool, etc Fixed SGA Aka – Shared Global Area

4. Database Buffer Cache Least-Recently-Used (LRU) buffer of data blocks Oracle checks the buffer before hitting the disk (cache hit vs. cache miss) Variable Cache Sizes

5. Shared Pool Library Cache Shared & Private SQL Areas PL/SQL Procedures and Packages Control Structures (locks, cache handles, etc) Accessible to All Users Data Dictionary Cache Accessed so often, requires it’s own cache Stores information as rows instead of data blocks

6. Large Pool Optional Memory Area Provides Large Memory Allocations Session Memory I/O Server Process Oracle Backup/Restore Operations

7. Java Pool Used for session-specific Java code and data Used differently depending on server configuration

8. Redo Buffer Circular Buffer holding change data Redo Entries Allows undo of INSERT, UPDATE, DELETE, CREATE, ALTER, or DROP Uses? Database Recovery!

9. Streams Pool Memory used for Oracle Streams If not defined, automatically created

10. SGA - Configuration Oracle Treats Memory as Granules SGA_MAX_SIZE = Maximum amount of memory Oracle can use Automatic Shared Memory Management SGA_TARGET = Total to be dynamically shared between subcomponents STATISTICS_LEVEL = TYPICAL or ALL

11. SGA – Configuration Cont. DB_CACHE_SIZE - The size of the cache of standard blocks. LOG_BUFFER - The number of bytes allocated for the redo log buffer. SHARED_POOL_SIZE - The size in bytes of the area devoted to shared SQL and PL/SQL statements. LARGE_POOL_SIZE - The size of the large pool. JAVA_POOL_SIZE - The size of the Java pool.

12. Program Global Area (PGA) Data and control information for a server process Exclusive, Non-Shared Contents: Private SQL Area Session Memory SQL Work Areas (Sorts, Hash-Join)

13. Software Code Area (SCA) Memory used for running code or code to be run Exclusive and Protected Area for Oracle code

14. References Oracle Database Concepts Oracle Database Admin Guide Oracle Database Performance Tuning Guide Oracle Database Application Developers Guide http://www.dbasupport.com/oracle/ora10g/s pfile01.shtml http://www.dba- oracle.com/tips_oracle_spfile_example.htm Oracle Tuning: The Definitive Reference