OraQA » Architecture http://oraqa.com Oracle Question and Answer Tue, 06 Jul 2010 00:08:52 +0000 http://wordpress.org/?v=2.8.4 en hourly 1 What are datafiles? http://oraqa.com/2006/11/05/what-are-datafiles/ http://oraqa.com/2006/11/05/what-are-datafiles/#comments Mon, 06 Nov 2006 06:35:10 +0000 Eddie Awad http://oraqa.com/2006/11/05/what-are-datafiles/ Every Oracle database has one or more physical datafiles. The datafiles contain all the database data. The data of logical database structures, such as tables and indexes, is physically stored in the datafiles allocated for a database.

  • A datafile can be associated with only one database.
  • Datafiles can have certain characteristics set to let them automatically extend when the database runs out of space.
  • One or more datafiles form a logical unit of database storage called a tablespace.

Data in a datafile is read, as needed, during normal database operation and stored in the memory cache of Oracle. Modified or new data is not necessarily written to a datafile immediately. To reduce the amount of disk access and to increase performance, data is pooled in memory and written to the appropriate datafiles all at once.

Sources and resources:

]]> http://oraqa.com/2006/11/05/what-are-datafiles/feed/ 0 What is the difference between a database and an instance? http://oraqa.com/2006/02/02/what-is-the-difference-between-a-database-and-an-instance/ http://oraqa.com/2006/02/02/what-is-the-difference-between-a-database-and-an-instance/#comments Thu, 02 Feb 2006 14:59:33 +0000 Eddie Awad http://oraqa.com/2006/02/02/what-is-the-difference-between-a-database-and-an-instance/ To understand the difference between a database and an instance, we need to know the basic definition of each and the relationship between them.

Definition:

  • A database is a set of files stored on disk.
  • An instance is a collection of Oracle background processes and shared memory.

Relationship:

  • An instance can mount and open one and only one database.
  • A database may be mounted and opened by one or more instances.

For example, in the case of Real Application Clusters (or RAC) a database is usually mounted and opened by many instances.

Related documentation: Instance, Database

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