A mode in which Oracle saves the entire redo log. As redo log files are filled, they are copied to another location, known as the archive log destination, for safekeeping. Running a database in archive log mode allows all committed changes to be recovered in the event of a failure.
Before images
Before images are copies of data that Oracle makes before a change. When you insert, update, or delete data, Oracle records the before image of each modified block in a rollback segment. This information is used in the event that you subsequently rollback your change.
Checkpoint
A number recorded in a database’s control file that represents the highest redo log number for which changes have already been written back to the data files.
Conventional path
An export mode where the data is retrieved from the database using an SQL query and standard SQL processing. See direct path.
Crash recovery
The process of redoing changes that were lost during a system crash because the affected data blocks were contained only in memory. During crash recovery, the redo log files are read and the changes are reapplied to the data files.
Data file
Used to denote a file used to store user data. Data files may contain table data, index data, or stored code.
Database
A collection of data that is treated as a unit. In practical terms, a database is a set of physical data files, control files, and redo log files.
Direct path
An export mode where data is retrieved directly from the database buffer cache, and where SQL processing is bypassed. See conventional path.
Flat file
A file, often a text file, containing records that must be read sequentially, from beginning to end.
Instance
A set of memory structures and background processes that operate against an Oracle database. Database users (programs that you run) communicate with an Oracle instance (background processes), and the instance does the actual work of reading and writing data to and from the database files. Using Oracle Parallel Server, it is possible to have multiple instances simultaneously operating against a single database.
Legacy
An old system that is based on out-of-date technology.
License high water mark
The largest number of users that have been connected to the database at one time since the database was last opened.
Locally managed tablespace
A tablespace for which the data dictionary is not used to keep track of the extents that have been allocated to objects in that tablespace. Instead, the tablespace file itself contains this information. Locally managed tablespaces are a new feature in Oracle8i, and allow tablespace files to be moved between databases.
Media recovery
The process of recovering a datafile by applying changes from the archived redo log files.
Oracle Parallel Server
Oracle Parallel Server is an option that allows many instances to open one database. In the right environment, Oracle Parallel Server can provide both scalability, and high-availability.
SELECT
The SQL command used to retrieve data from a database.
Serizable
Refers to a transaction that maintains a read-consistent view of the data throughout the duration of the transaction. This means that all statements in the transaction see the database as it was when the transaction began. Changes made by other transactions are not seen until the serializable transaction is committed.
SID
An abbreviation for system identifier. The system identifier is the name that identifies an Oracle instance.
SQL
An abbreviation for Structured Query Language. It provides a set of commands that can be used to add data to a database, retrieve that data, and update it. Relational database vendors universally support SQL, often pronounced "sequel."
System crash
A system crash is when your Operating system software, or your database server software, suddenly stops running because of an error, or because of a bug triggered by an unusual set of circumstances.
Trace file
A text file that Oracle generates, usually to record information that might be helpful in tracking down the cause of an error. Trace files are also generated as a result of the ALTER DATABASE BACKUP CONTROLFILE TO TRACE command.
Usenet
A networked collection of discussion groups that you can access via the Internet.
