Dynamic performance views

[mewa]

Hi,
I prepare myself to Fundametals I exam with Couchman book. In the first chapter of the book I found information that dynamic performance views are not a part of data dictionary (data dictionary consists of static views only). In the second chapter I found the information that they ARE a part of data dictionary.
What is a correct understanding of data dictionary?

mewa

 

[aryeh1010]

The data dictionary is the actual tables that Oracle uses to manage its structure internally.

The dynamic performance views (v$ views) show you what is going on in the instance, but they are not part of the data dictionary, as they are only views. Some views would be v$sysstat, v$sort_segment, etc..

There are also data dictionary views that read from the data dictionary, but are not part of it: v$datafile, v$tablespace, v$logfile, etc.

Anything that is a view isn't part of the data dictionary, which is made up of tables. They just let you peek inside. Oracle doesn't want to take a chance and allow people direct access to the data dictionary where they could cause problems.

 

[mewa]

Thanks for you replay. It clarifies what is a data dictionary for me.
Now, another question is how to distinquish between data dictionary views and dynamic performance views if they both use the v$something name convention.
From Couchman book I understood the data dictionary views usually consist from two parts: the scope and the theme, e.g. all_users.
From your replay I quess v$logfile is a data dictionary view while v$sysstat is a dynamic performance view. How to find out what kind of view a view is?

mewa

 

[aryeh1010]

I think you should just use common sense, any v$ view with stat, waits, usage, or any other word that indicates some kind of action I would say is a dynamic performance view.

Anything that pertains to an object, v$logfile, v$datafile, v$database, v$instance would probably be a data dictionary view.

For example:
v$rollname - data dictionary view, because it gives the name and number of rollback segments.

v$rollstat - dynamic performance view, because it shows what is happening with the rollback segments right now, size ,extends, wraps, etc.

The main data dictionary views are the DBA, USER, and ALL views.

The scope of DBA is the entire database. The scope of USER is for the schema/user (interchangeable terms). The scope of ALL is for all of the objects owned by the user, plus any objects that the user has privileges on in other schemas.

Hope this helps

 

[mewa]

Thanks for the explanation.