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Oracle in a Nutshell
book

Oracle in a Nutshell

by Rick Greenwald, David C. Kreines
December 2002
Intermediate to advanced content levelIntermediate to advanced
928 pages
85h 29m
English
O'Reilly Media, Inc.
Content preview from Oracle in a Nutshell

How Dynamic Data Dictionary Views Are Built

Unlike the static data dictionary views, which are views on existing tables, the dynamic performance data dictionary views are views on a set of tables that do not physically exist in the database; instead, they are actually views on X$ tables, which are representations of internal memory structures in the Oracle instance. For example:

  • V$DATABASE is a public synonym for the view SYS.V_$DATABASE.

  • SYS.V_$DATABASE is a view on SYS.V$DATABASE.

  • V$DATABASE is a view on the memory structure X$KCCDI.

The exact specification of how the V$ views are built is maintained within the Oracle kernel. The view V$FIXED_VIEW_DEFINITION defines all V$ views as views based upon the X$ tables.

How these views are built is important to understanding how they work. Initially defined within the Oracle kernel, these hardcoded V$ tables are accessible once the instance has been started or once the database has been mounted. Once the database is opened, the normal SQL processing takes over, and the public synonyms referencing the views are used. With public synonyms, the same name is available whether you are CONNECTed INTERNAL before the database is opened, or are connected as a user with DBA privileges after the database is opened.

The relatively few V$ views that are available only once the database is open turn out to be true views, based upon X$ or other V$ tables.

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Publisher Resources

ISBN: 0596003366Errata Page