Summarize the single instance architecture	A user interacts with a user process. A user process interacts with a server process. A server process interacts with an instance. An instance interacts with a database.
Distributed Systems Architecture	Real Application Clusters (RAC), where multiple instances open one database. Streams, where multiple Oracle servers propagate transactions between each other. Data guard, where a primary database updates a standby database.
Required SGA data structures	The database buffer cache. The log buffer. The shared pool
Optional SGA data structures	A large pool. A Java pool. A Streams pool
Characteristics of PGA	Is the memory allocated for user sessions. Is unshareable. Each session will have its own private PGA.
Characteristics of Database Buffer Cache	Stores blocks of data required to execute DML statements. Its size is critical for performance, can be adjusted dynamically (no downtime required) and can be automatically managed.
What is the Log Buffer?	The log buffer is a small, short-term staging area for change vectors before they are written to the redo log on disk.
Characteristics of Log Buffer	It's small compared to other memory structures. It is not possible to create a log buffer smaller than default. Cannot be resized without restarting the instance.
Are substructures of the Shared Pool	The library cache. The data dictionary cache. The PL/SQL area. The SQL query and PL/SQL function result caches.
Can the Log Buffer be resized?	No, the Log Buffer size is fixed at startup, and cannot be resized without restarting the instance.
Can the Shared pool be resized?	Yes, the pool size is dynamic and can be automatically managed.
What is the Library Cache?	Is a memory area for storing recently executed code, in its parsed form.
What is the purpose of the Library Cache?	Caching parsed code so that it can be reused without reparsing, improving performance.
What is the Data Dictionary Cache?	Is a memory area for storing recently used object definitions: descriptions of tables, indexes, users, and other metadata definitions.
What is the purpose of the Data Dictionary Cache?	Keeping such definitions in memory in the SGA, where they are immediately accessible to all sessions, rather than each session having to read them repeatedly from the data dictionary on disk, enhances parsing performance.
What is the PL/SQL Area?	Is a memory area for storing PL/SQL objects as source code and also in their compiled form.
What is the purpose of the PL/SQL Area?	Prevent repeated reading of stored PL/SQL objects.
What are the SQL Query and PL/SQL Function Result Cache?	Are memory areas for storing query and functions results, so the next time they are executed the server can retrieve the cached result.
What is the Large Pool?	The large pool is an optional area that, if created, will be used automatically by various processes that would otherwise take memory from the shared pool.
Uses of the Large Pool	One major use of the large pool is by shared server processes. Parallel execution servers will also use the large pool, if there is one. In the absence of a large pool, these processes will use memory on the shared pool.
Can the Large Pool be resized?	Yes, the large pool size is dynamic and can be automatically managed.
What is the Java Pool?	Is a memory area used for heap space needed to instantiate the Java objects.
Can the Java Pool be resized?	Yes, the java pool size is dynamic and can be automatically managed.
View with information about Memory Structures	v$sga_dynamic_components
What is SMON?	The system monitor, initially has the task of mounting and opening a database.
Tasks of SMON	SMON mounts a database by locating and validating the database controlfile. It then opens a database by locating and validating all the datafiles and online log files. Once the database is opened and in use, SMON is responsible for various housekeeping tasks, such as collating free space in datafiles.
What is PMON?	The process monitor, monitors all the server processes and detects any problems with the sessions.
Tasks of PMON	If a session has terminated abnormally, PMON will destroy the server process, return its PGA memory to the operating system’s free memory pool, and roll back any incomplete transaction that may have been in progress.
If a session terminates abnormally, what will happen to an active transaction?	It will be rolled back, by the PMON background process.
What is DBWn?	The database writer, writes dirty buffers from the database buffer cache to the datafiles.
Characteristics of DBWn	There can be up to 20 database writers. Default is one DBW per 8 CPU's. Writes with a very lazy algorithm.
What will cause DBWn to write?	No free buffers, too many dirty buffers, a three second timeout, or a checkpoint.
What does DBWn do when a transaction is committed?	It does absolutely nothing.

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