Explanation/Reference:
Explanation:
You can use the SQL Performance Analyzer to analyze the SQL performance impact of any type of system
change. Examples of common system changes include:
* Database upgrades
* Configuration changes to the operating system, hardware, or database
* Database initialization parameter changes
* Schema changes, such as adding new indexes or materialized views
* Gathering optimizer statistics
* SQL tuning actions, such as creating SQL profiles
http://docs.oracle.com/cd/B28359_01/server.111/b28318/intro.htm#CNCPT961

Explanation
Manually Sized SGA Components that Use SGA_TARGET Space
SGA Component, Initialization Parameter
/ The log buffer
LOG_BUFFER
/ The keep and recycle buffer caches
DB_KEEP_CACHE_SIZE
DB_RECYCLE_CACHE_SIZE
/ Nonstandard block size buffer caches
DB_nK_CACHE_SIZE
Note:
* In addition to setting SGA_TARGET to a nonzero value, you must set to zero all initialization parameters listed in the table below to enable full automatic tuning of the automatically sized SGA components.
* Table, Automatically Sized SGA Components and Corresponding Parameters

Explanation/Reference:

Explanation/Reference:
Explanation:
utlrp.sql and utlprp.sql
The utlrp.sql and utlprp.sql scripts are provided by Oracle to recompile all invalid objects in the database.
They are typically run after major database changes such as upgrades or patches. They are located in the
$ORACLE_HOME/rdbms/admin directory and provide a wrapper on the UTL_RECOMP package. The utlrp.sql script simply calls the utlprp.sql script with a command line parameter of "0". The utlprp.sql accepts a single integer parameter that indicates the level of parallelism as follows.
0 - The level of parallelism is derived based on the CPU_COUNT parameter.
1 - The recompilation is run serially, one object at a time.
N - The recompilation is run in parallel with "N" number of threads.
Both scripts must be run as the SYS user, or another user with SYSDBA, to work correctly.
References: