Tuesday, April 17, 2007

Oracle9i DBA -- Database: Fundamentals I (12)

Managing Tables


  • The TZ environment variable can be used to decide the how the date will be displayed.
  • Each row in the table consists of a Row header (store the number of columns in a row) and Row Data (stores the column length and value).
  • A ROWID is composed of

    O Datafile number : Is assigned to each data object, such as table or index when it is created, and it is unique within the database.

    O Relative file number : is unique to each file within a tablespace

    O Block number : Represents the position of the block, containing the row, within the file.

    O Row number : Identifies the position of the row directory slot in the block header.

  • The portioning methods available in tables are Range, Hash, List and Composite. Range portioning is useful for tables with a range of value. Hash portioning is done using Hash algorithm. When all the values that are to be stored in a column are known, list partitioning can be used. Composite partitioning is a combination of hash and range partitioning.
  • The value of the parameter COMPATIBLE must be set to Oracle 8.1 or highter to use ROWID.
  • PCTFREE, NEXT, MINEXENTS can be modified after table creation.
  • Row Migration occurs due to low PCTFREE value. Row chaining the row is divided into smaller chunks. Row migration the entire row is moved to a new block.

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