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Mapping components

The mapping components in the System Global Area (SGA) and Oracle's representation of these components are described in this section. You will need an understanding of these components to interpret the mapping information in Oracle's dynamic performance views.

The mapping information in Oracle's dynamic performance views consists of:

• File components

  A mapping file component is a mapping structure describing a file. It provides a set of attributes for a file, including the file's size, number of extents, and type. File components are exported to the user through V$MAP_FILE.

• File extent components

  A mapping file extent component describes a contiguous group of blocks residing on one element. The description specifies the device offset, the extent size, the file offset, the extent type (Data or Parity), and the name of the element where the extent resides.

• Element components

  A mapping element component is a mapping structure that describes a storage component within the I/O stack. Elements can be mirrors, stripes, partitions, RAID5, concatenated elements, and disks.

  This component contains information about the element's mapping structure, such as the element's size, type, number of subelements, and a brief description. Element components are exported to the user through V$MAP_ELEMENT.

• Subelement components

  A mapping subelement component describes the link between an element and the next element in the I/O stack. The subelement component contains the subelement number, size, the element name for the subelement, and the element offset. Subelement components are exported to the user through V$MAP_SUBELEMENT.

These four types of mapping components completely describe the mapping information for an Oracle instance.