source : http://docs.oracle.com/ This chapter discusses the processes in an Oracle database. This chapter contains the following sections: Introduction to Processes Overview of Client Processes Overview of Server Processes Overview of Background Processes   Introduction to Processes A process is a mechanism in an operating system that can run a series of steps. The process execution architecture depends on the operating system. For example, on Windows an Oracle background process is a thread of execution within a process. On Linux and UNIX, an Oracle process is either an operating system process or a thread within an operating system process. Processes run code modules. All connected Oracle Database users must run the following modules to access a database instance: Application or...

source : http://docs.oracle.com This chapter discusses the memory architecture of a database instance. This chapter contains the following sections: Introduction to Oracle Database Memory Structures Overview of the User Global Area Overview of the Program Global Area (PGA) Overview of the System Global Area (SGA) Overview of Software Code Areas See Also: Oracle Database Administrator's Guide for instructions for configuring and managing memory   Introduction to Oracle Database Memory Structures When an instance is started, Oracle Database allocates a memory area and starts background processes. The memory area stores information such as the following: Program code Information about each connected session, even if it is not currently active Information needed du...

source : http://docs.oracle.com This chapter explains the nature of an Oracle database instance, the parameter and diagnostic files associated with an instance, and what occurs during instance creation and the opening and closing of a database. This chapter contains the following sections: Introduction to the Oracle Database Instance Overview of Database Instance Startup and Shutdown Overview of Checkpoints Overview of Instance Recovery Overview of Parameter Files Overview of Diagnostic Files   Introduction to the Oracle Database Instance A database instance is a set of memory structures that manage database files. A database is a set of physical files on disk created by the CREATE DATABASE statement. The instance manages its associated data and serves the users of the database. ...

source : http://docs.oracle.com This chapter describes the nature of and relationships among logical storage structures. These structures are created and recognized by Oracle Database and are not known to the operating system. This chapter contains the following sections: Introduction to Logical Storage Structures Overview of Data Blocks Overview of Extents Overview of Segments Overview of Tablespaces   Introduction to Logical Storage Structures Oracle Database allocates logical space for all data in the database. The logical units of database space allocation are data blocks, extents, segments, and tablespaces. At a physical level, the data is stored in data files on disk (see Physical Storage Structures). The data in the data files is stored in operating system blocks. Figure 1...

source : http://docs.oracle.com This chapter describes the primary physical database structures of an Oracle database. Physical structures are viewable at the operating system level. This chapter contains the following sections: Introduction to Physical Storage Structures Overview of Data Files Overview of Control Files Overview of the Online Redo Log   Introduction to Physical Storage Structures One characteristic of an RDBMS is the independence of logical data structures such as tables, views, and indexes from physical storage structures. Because physical and logical structures are separate, you can manage physical storage of data without affecting access to logical structures. For example, renaming a database file does not rename the tables stored in it. An Oracle database is a s...

source : http://docs.oracle.com/ This chapter defines a transaction and describes how the database processes transactions. This chapter contains the following sections: Introduction to Transactions Overview of Transaction Control Overview of Transaction Guard Overview of Application Continuity Overview of Autonomous Transactions Overview of Distributed Transactions   Introduction to Transactions A transaction is a logical, atomic unit of work that contains one or more SQL statements. A transaction groups SQL statements so that they are either all committed, which means they are applied to the database, or all rolled back, which means they are undone from the database. Oracle Database assigns every transaction a unique identifier called a transaction ID. All Oracle transactions ob...

source : http://docs.oracle.com This chapter explains how Oracle Database maintains consistent data in a multiuser database environment. This chapter contains the following sections: Introduction to Data Concurrency and Consistency Overview of Oracle Database Transaction Isolation Levels Overview of the Oracle Database Locking Mechanism Overview of Automatic Locks Overview of Manual Data Locks Overview of User-Defined Locks Introduction to Data Concurrency and Consistency In a single-user database, a user can modify data without concern for other users modifying the same data at the same time. However, in a multiuser database, statements within multiple simultaneous transactions may update the same data. Transactions executing simultaneously must produce meaningful and consistent results...

source : http://docs.oracle.com SQL explains the Structured Query Language (SQL) language and how the database processes SQL statements. This chapter explains how Procedural Language/SQL (PL/SQL) or Java programs stored in the database can use SQL. This chapter includes the following topics: Introduction to Server-Side Programming Overview of PL/SQL Overview of Java in Oracle Database Overview of Triggers See Also: SQL Introduction to Server-Side Programming In a nonprocedural language such as SQL, the set of data to be operated on is specified, but not the operations to be performed or the manner in which they are to be carried out. In a procedural language program, most statement execution depends on previous or subsequent statements and on control structures, such as loops or condit...

source : http://docs.oracle.com/ This chapter provides an overview of the Structured Query Language (SQL) and how Oracle Database processes SQL statements. This chapter includes the following topics: Introduction to SQL Overview of SQL Statements Overview of the Optimizer Overview of SQL Processing Introduction to SQL SQL (pronounced sequel) is the set-based, high-level declarative computer language with which all programs and users access data in an Oracle database. Although some Oracle tools and applications mask SQL use, all database tasks are performed using SQL. Any other data access method circumvents the security built into Oracle Database and potentially compromises data security and integrity. SQL provides an interface to a relational database such as Oracle Database. SQL unifie...

source : http://docs.oracle.com The central set of read-only reference tables and views of each Oracle database is known collectively as the data dictionary. The dynamic performance views are special views that are continuously updated while a database is open and in use. This chapter contains the following sections: Overview of the Data Dictionary Overview of the Dynamic Performance Views Database Object Metadata Overview of the Data Dictionary An important part of an Oracle database is its data dictionary, which is a read-only set of tables that provides administrative metadata about the database. A data dictionary contains information such as the following: The definitions of every schema object in the database, including default values for columns and integrity constraint information ...