December 2002
Intermediate to advanced
928 pages
85h 29m
English
Content preview from Oracle in a NutshellBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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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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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.