Database Architecture An Oracle database server consists of an Oracle database and an Oracle instance. Oracle Database architecture is based on physical and logical structures. Oracle Database Physical Structure Oracle database consists of physical files to store information. Basically there are three types of physical files required for database: Core Files: Data Files [...]
Archive for the ‘Storage Architecture’ Category
7 Apr
UNDO Tablespace
Undo Segment An undo segment is used to save the old value (undo data) when a process changes data in a database. It stores the location of the data and the data as it existed before being modified. The header of an undo segment contains a transaction table where information about the current transactions using [...]
3 Apr
Automatic segment space management
Automatic Segment-Space Management • Bitmap segments contain a bitmap that describes the status of each block in the segment with respect to its available space. • The map is contained in a separate set of blocks referred to as bitmapped blocks (BMBs). • When inserting a new row, the server searches the map for a [...]
3 Apr
Tablespaces
Tablespaces The data in an Oracle database are stored in tablespaces. • An Oracle database can be logically grouped into smaller logical areas of space known as tablespaces. • A tablespace can belong to only one database at a time. • Each tablespace consists of one or more operating system files, which are called data [...]
3 Apr
Redo Logs
Redo log files provide the means to redo transactions in the event of a database failure. Every transaction is written synchronously to the redo log files in order to provide a recovery mechanism in case of media failure. (With exceptions such as: direct loads and direct reads done with the NOLOGGING option.) This includes transactions [...]
2 Apr
CONTROL FILE
The control file is a small binary file necessary for the database to start and operatesuccessfully. Each control file is associated with only one Oracle database. Before a database is opened, the control file is read to determine if the database is in a valid state to use. A control file is updated continuously by [...]
29 Mar
Temporary Tablespace DDL
What are TEMPFILES? Unlike normal data files, TEMPFILEs are not fully initialised (sparse). When you create a TEMPFILE, Oracle only writes to the header and last block of the file. This is why it is much quicker to create a TEMPFILE than to create a normal database file. Dropping / Recreating Temporary Tablespace Method Keep [...]
10 Mar
Types of Tables
Regular table: A regular table (generally referred to as a “table”) is the most commonly used form of storing user data. This is the default table and is the main focus of discussion in this lesson. A database administrator has very limited control over the distribution of rows in a table. Rows can be stored [...]
10 Mar
Row Format
Oracle stores each row of a database table containing data for less than 256 columns as one or more row pieces. If an entire row can be inserted into a single data block, then Oracle stores the row as one row piece. However, if all of a row’s data cannot be inserted into a single [...]
10 Mar
ROWID Format
ROWID Format Extended ROWID An extended ROWID needs 10 bytes of storage on disk and is displayed by using 18 characters. It consists of the following components: •Data object number: Is assigned to each data object, such as table or index when it is created, and it is unique within the database •Relative file number: [...]
