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Performance Tuning (Oracle) - Glossary

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One of the biggest responsibilities of a DBA is to ensure that the Oracle database is tuned properly. The Oracle RDBMS is highly tunable and allows the database to be monitored and adjusted to increase its performance. One should do performance tuning for the following reasons:
  1. The speed of computing might be wasting valuable human time (users waiting for response);
  2. Enable your system to keep-up with the speed business is conducted; and
  3. Optimize hardware usage to save money (companies are spending millions on hardware).
Asynchronous
A process where a command is submitted and the submitter does not wait for a response from the recipient of the command.
B* tree
An index made up of a number of levels of leaf nodes. Each leaf node contains a range of values and pointers to a more detailed leaf node. The lowest leaf node points to a page of index values and the ROWIDs of the rows associated with them.
Bitmapped Index
Uses individual bits in an index entry to identify the value of an entry. A bitmapped index works best when there are a limited number of values for an index.
Bitwise comparison
A situation where the Oracle database compares two values bit by bit, instead of character by character (also known as byte by byte).
Constraint
A constraint is a database rule that you define within the database to enforce certain conditions regarding the data that is stored in the database tables.
Data Warehouse
A type of database that is used for analysis of data. The data warehouse frequently has a different type of structure a star schema as opposed to a standard normalized schema and is also frequently separate from an organization's transaction database.

Execution Plan
A description of the steps the Oracle database will take to retrieve and select the data requested by a query.
Online Analytical Processing (OLAP)
A type of computing that delivers summary data organized by a variety of attributes, such as time or location. OLAP is used a lot with data warehouses.
Optimizer
Built-in database software that determines the most efficient way to execute a SQL statement. The query optimizer is made up of the query transformer, the estimator, and the plan generator. The optimizer generates a set of potential execution plans for SQL statements, estimates the cost of each plan, calls the plan generator to generate the plan, compares the costs, and chooses the plan with the lowest cost. The database uses this approach when the data dictionary has statistics for at least one of the tables accessed by the SQL statements.
Package
A group of PL/SQL procedures that are combined into a single logical grouping. The package header contains the interface description for the procedures, whereas the package body contains the actual code for the procedures in the package.
Parallelism
The ability of the Oracle database to divide a single request into multiple tasks that will execute in parallel, which usually results in reduced execution time.
Primary key
One or more columns that define a unique row in a table. A table can contain only one primary key.
Procedure
Uses PL/SQL code and syntax to implement a logical operation.
ROWID
An internal value that uniquely identifies each individual row in an Oracle database.
Table constraint
Constraints that apply to more than one column.
Type definition
Defines an Oracle object type.
Unique key
A second primary key in a table. A table can contain more than one unique key.
Wrapper
Code that wraps a type of logic with some other code to make a cleaner interface.