CHAPTER 10Data Dictionary Basics

Data Dictionary• Information regarding objects and events within the

database.• Super critical that as a DBA or developer you know how to

leverage the information within the data dictionary.• The data dictionary is always a good place to look when

troubleshooting or determining facts about your database.• This chapter gives you a foundation for understanding and

querying the data dictionary.

Data Dictionary Contents• Data dictionary objects owned by SYS• Static views• Dynamic views

Static Views• There are three types or levels of static views:

• USER• ALL• DBA

• USER/ALL/DBA views contain metadata (information) describing the physical makeup of the database.

• Use these views to view the structure of the database and information about users and corresponding objects.

• Examples: DBA_USERS, DBA_TABLES, DBA_INDEXES, DBA_CONSTRAINTS, DBA_TABLESPACES, DBA_SEGMENTS, DBA_EXTENTS, and so on.

Creating Static Views

Dynamic Views• Dynamic performance data-dictionary views are often

referred to as the V$ and GV$ views. • Continuously updated by Oracle and reflect the current

condition of the instance and database.• Dynamic views are critical for diagnosing real-time

performance issues.

Creating Dynamic Views

Viewing View Creation Details• Query v$fixed_view_definition

select

view_definition

from v$fixed_view_definition

where view_name='V$CONTROLFILE';

Derivable Database Documentation• DBA_OBJECTS• DICTIONARY• DICT_COLUMNS

Logical and Physical Database Structures

Relationships of Common Data Dictionary Views

Database Space-Management Views• V$DATABASE• DBA/ALL/USER_USERS• DBA/USER_TABLESPACES• DBA_DATA_FILES• DBA/USER_FREE_SPACE• V$DATAFILE• V$DATAFILE_HEADER• DBA/ALL/USER_TABLES• DBA/ALL/USER_INDEXES• Many, many, more...

Displaying User Information• Currently connected users• Current SQL being executed by users• User accounts in the database

Currently Connected User Info

SQL> show user;

SQL> select * from user_users;

SQL> select name from v$database;

SQL> select instance_name, host_name from v$instance;

select

sys_context('USERENV','CURRENT_USER') usr

,sys_context('USERENV','AUTHENTICATION_METHOD') auth_mth

,sys_context('USERENV','HOST') host

,sys_context('USERENV','INSTANCE_NAME') inst

from dual;

Users Currently Logged In

select

count(*)

,username

from v$session

group by username;

Currently Executing SQLExample 1:

select

a.sid

,a.username

,b.sql_text

from v$session a

,v$sqltext_with_newlines b

where a.sql_id = b.sql_id

order by

a.username

,a.sid

,b.piece;

Currently Executing SQL

Example 2:

select s.username,s.sid,s.serial#,s.last_call_et/60 mins_running,q.sql_text

from v$session s join v$sqltext_with_newlines q on s.sql_address = q.address

where status='ACTIVE'

and type <>'BACKGROUND'

and last_call_et> 60 order by sid,serial#,q.piece;

User Accountsset lines 132

col username form a15

col default_tablespace form a18

col temporary_tablespace form a20

col account_status form a16

--

select

username

,default_tablespace

,temporary_tablespace

,account_status

,created

,lock_date

from dba_users

order by 1;

Viewing Table Information

select

a.table_name

,b.created

,b.last_ddl_time

,a.last_analyzed

from user_tables a, user_objects b

where a.table_name = b.object_name;

Displaying Object Disk-Space UsageUNDEFINE owner

COL summer FORM 999,999.999

SET LINES 132 TRIMSPOOL ON PAGES 100

SPO space.txt

SELECT

segment_name

,partition_name

,tablespace_name

,segment_type

,SUM(bytes)/1024/1024 summer

FROM dba_extents

WHERE owner = UPPER('&&owner')

GROUP BY segment_name,partition_name,tablespace_name,segment_type

ORDER BY segment_name,partition_name;

SPO OFF;

Displaying Table Row CountsUNDEFINE user

SPOOL tabcount_&&user..sql

SET LINESIZE 132 PAGESIZE 0 TRIMSPO OFF VERIFY OFF FEED OFF TERM OFF

SELECT

'SELECT RPAD(' || '''' || table_name || '''' ||',30)'

|| ',' || ' COUNT(*) FROM &&user..' || table_name || ';'

FROM dba_tables

WHERE owner = UPPER('&&user')

ORDER BY 1;

SPO OFF;

SET TERM ON

@@tabcount_&&user..sql

SET VERIFY ON FEED ON

Manually Generating StatisticsSQL> exec dbms_stats.gather_table_stats(ownname=>'INV',-

tabname=>'F_SALES',-

cascade=>true,estimate_percent=>20,degree=>4);

SQL> exec dbms_stats.gather_schema_stats(ownname => 'INV',-

estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,-

degree => DBMS_STATS.AUTO_DEGREE,-

cascade => true);

Displaying Indexes for a Table• Troubleshooting performance issues.• What indexes exist and on what columns?

select

a.index_name

,a.column_name

,b.status

,b.index_type

,a.column_position

from user_ind_columns a

,user_indexes b

where a.table_name = upper('&table_name')

and a.index_name = b.index_name

order by a.index_name, a.column_position;

Displaying Table Constraints• Troubleshooting or determining what types of constraints are in place.

select table_name ,(case constraint_type

when 'P' then 'Primary Key'

when 'R' then 'Foreign Key'

when 'C' then 'Check'

when 'U' then 'Unique'

when 'O' then 'Read Only View'

when 'V' then 'Check view'

when 'H' then 'Hash expression'

when 'F' then 'REF column'

when 'S' then 'Supplemental logging'

end) cons_type

,constraint_name cons_name ,search_condition check_cons ,status

from dba_constraints

where owner like upper('&owner')

and table_name like upper('&table_name')

order by cons_type;

Showing Primary-Key and Foreign-Key Relationships• Sometimes need to determine for child table FKs what are associated PKs and

visa versa.

select

a.constraint_type cons_type

,a.table_name child_table

,a.constraint_name child_cons

,b.table_name parent_table

,b.constraint_name parent_cons

,b.constraint_type cons_type

from dba_constraints a

,dba_constraints b

where a.owner = upper('&owner')

and a.table_name = upper('&table_name')

and a.constraint_type = 'R'

and a.r_owner = b.owner

and a.r_constraint_name = b.constraint_name;

Displaying Granted Roles

select

username

,granted_role

from user_role_privs;

select

grantee

,granted_role

from dba_role_privs

where grantee = upper('&grantee')

order by grantee;

Displaying System Privileges• Query these dba_sys_privs when troubleshooting

privilege issues.

select

grantee

,privilege

,admin_option

from dba_sys_privs

where grantee = UPPER('&grantee')

order by privilege;

Displaying Object Privileges• Query data dictionary when diagnosing object access

issues.

select

owner

,table_name

,grantor

,privilege

from user_tab_privs_recd;

Displaying Object Dependencies• Before dropping an object, it’s useful to determine which

objects might have dependencies on the object to be dropped.

select '+' || lpad(' ',level+2) || type || ' ' || owner || '.' || name dep_tree

from dba_dependencies

connect by prior owner = referenced_owner and prior name = referenced_name

and prior type = referenced_type

start with referenced_owner = upper('&object_owner')

and referenced_name = upper('&object_name')

and owner is not null;

V$ and GV$ Views• The V$ and GV$ views are used for performance tuning

and database troubleshooting.• These are covered more in Chapter 22 Database

Troubleshooting.

Summary• DBAs and developers must understand the data

dictionary architecture and how to leverage the information to troubleshoot and maintain database environments.

• Main focus of this chapter was the static data dictionary views.

• Dynamic views covered more later in the book in the database troubleshooting chapter.