Oracle SQL Syntax: V$ views

I've noticed that Oracle comes with some special tables/views (e.g. V$SESSION) that are not contained in dba_tables nor in dba_views.

Why is that?

Can someone开发者_开发百科 explain when tables or views are part of dba_tables / dba_views and when not?

All views are listed in DBA_VIEWS.

Oracle's V$ objects are actually public synonyms (and they do appear in DBA_SYNONYMS). V$SESSION is a synonym for SYS.V_$SESSION which does appear in DBA_VIEWS. In general, the V$ objects are public synonyms for views in the SYS schema with the prefix V_$ and the GV$ are public synonyms for views in the SYS schema with the prefix GV_$.

Throughout its operation, Oracle Database maintains a set of virtual tables that record current database activity. These views are called dynamic performance views because they are continuously updated while a database is open and in use. The views, also sometimes called V$ views

...I'll let Oracle explain ;) Also see here.