Oracle maintains a set of virtual tables that record current database activity. These tables are called dynamic performance tables.

This post was written by Sriram Sanka in his blog.

Why the term “Fixed”?

Because They are fixed ..One cannot perform any DML , DDL or any operation other than “SELECT“,that’s why these views/Tables are known as Fixed.

sql> alter table x$ksmsp add sriram varchar2(30);
alter table x$ksmsp add sriram varchar2(30)
ERROR at line 1:
ORA-02030: can only select from fixed tables/views.

Oracle maintains some dynamic performance views which are dynamically created based on the “X$” tables.

Those are basically start with ‘V$’ and ‘GV$’ with one extra column “Instance_id”.

sql> desc v$fixed_table
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 NAME                                               VARCHAR2(30)
 OBJECT_ID                                          NUMBER
 TYPE                                               VARCHAR2(5)
 TABLE_NUM                                          NUMBER

sql> desc v$fixed_view_definition
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 VIEW_NAME                                          VARCHAR2(30)
 VIEW_DEFINITION                                    VARCHAR2(4000)

We can query of these views, to get more Info on these views

sql> select * from V$FIXED_VIEW_DEFINITION where view_name='V$SESSION';

VIEW_NAME                      VIEW_DEFINITION
------------------------------ --------------------------------------------------
V$SESSION                      select  SADDR , SID , SERIAL# , AUDSID , PADDR , U
                               SER# , USERNAME , COMMAND , OWNERID, TADDR , LOCKW
                               AIT , STATUS , SERVER , SCHEMA# , SCHEMANAME ,OSUS
                               ER , PROCESS , MACHINE , TERMINAL , PROGRAM , TYPE
                                , SQL_ADDRESS , SQL_HASH_VALUE, SQL_ID, SQL_CHILD
                               _NUMBER , PREV_SQL_ADDR , PREV_HASH_VALUE , PREV_S
                               QL_ID, PREV_CHILD_NUMBER , MODULE , MODULE_HASH ,
                               ACTION , ACTION_HASH , CLIENT_INFO , FIXED_TABLE_S
                               EQUENCE , ROW_WAIT_OBJ# , ROW_WAIT_FILE# , ROW_WAI
                               T_BLOCK# , ROW_WAIT_ROW# , LOGON_TIME , LAST_CALL_
                               ET , PDML_ENABLED , FAILOVER_TYPE , FAILOVER_METHO
                               D , FAILED_OVER, RESOURCE_CONSUMER_GROUP, PDML_STA
                               TUS, PDDL_STATUS, PQ_STATUS, CURRENT_QUEUE_DURATIO
                               ,P1TEXT,P1,P1RAW,P2TEXT,P2,P2RAW, P3TEXT,P3,P3RAW,
                               WAIT_CLASS_ID, WAIT_CLASS#,WAIT_CLASS,WAIT_TIME, S
                               ECONDS_IN_WAIT,STATE,SERVICE_NAME, SQL_TRACE, SQL_
                               TRACE_WAITS, SQL_TRACE_BINDS from GV$SESSION where
                                inst_id = USERENV('Instance')

1 row selected.

sql> select * from V$FIXED_VIEW_DEFINITION where view_name='V$FIXED_VIEW_DEFINITION';

VIEW_NAME                      VIEW_DEFINITION
------------------------------ --------------------------------------------------
                               VIEW_DEFINITION where inst_id = USERENV('Instance'

1 row selected.

ind> select * from V$FIXED_VIEW_DEFINITION
  2   where view_name='GV$FIXED_VIEW_DEFINITION';


These are permanent tables/views.The X$ tables are generated when ever you instance started.
These tables are accessible to the SYS User only.These ‘X$‘ are not even modifiable By the Super User ‘SYS‘.

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