Oracle's Data dictionary

First, Oracle's dictionary and Dynamic Data dictionary views can basically be divided into three levels.

1.x$ table

This section of the table is the basis for the operation of the Oracle database, which is dynamically created by the Oracle application when the database is started.

2.gv$ and v$ views

Starting with Oracle8, the gv$ view is introduced, which means global v$.

In addition to some exceptions, each v$ view has a corresponding gv$ view.

The gv$ view is generated to meet the needs of the OPS environment, where the query gv$ view returns all instance information, and each v$ view is based on the gv$ view, adding inst_id column creation, containing only the current connection instance information.

Note that each v$ view contains a similar statement:

where inst_id = USERENV (' Instance ')

Used to restrict the return of the current instance information.

We start with gv$fixed_table and v$fixed_table.

Sql> Select View_definition from v_$fixed_view_definition where view_name= ' v$fixed_table ';

View_definition

-------------------------------------------------------------------------------------- ----------------

Select NAME, object_id, TYPE, table_num from gv$fixed_table where inst_id = USERENV (' Instance ')

Here we see v$fixed_table based on gv$fixed_table creation.

Sql> Select View_definition from v_$fixed_view_definition where view_name= ' gv$fixed_table ';

View_definition

-------------------------------------------------------------------------------------- ------------------

Select Inst_id,kqftanam, Kqftaobj, ' TABLE ', indx from X$kqfta

UNION ALL

Select Inst_id,kqfvinam, Kqfviobj, ' VIEW ', 65537 from X$KQFVI

UNION ALL

Select Inst_id,kqfdtnam, Kqfdtobj, ' TABLE ', 65537 from X$KQFDT

So we found the Gv$fixed_table view creation statement, which is based on the x$ table.

3.gv_$,v_$ View and v$,gv$ synonyms

These views are created by Catalog.sql.

When Catalog.sql is running:

Create or Replace view v_$fixed_table as SELECT * from V$fixed_table;

Create or replace public synonym v$fixed_table for v_$fixed_table;

Create or Replace view gv_$fixed_table as SELECT * from Gv$fixed_table;

Create or replace public synonym gv$fixed_table for gv_$fixed_table;