Oracle data dictionary is stored inside the database where information about its purpose is to describe the operation and management of the internal database. For example, the owner of a table of data, creation time, your table space, user access rights, etc., this information can be found in the data dictionary. When data difficulties, it can help to provide information by querying the data dictionary.
A, Oracle Data Dictionary Overview
Oracle data dictionary name prefix and a suffix, using the "_" is connected, which represents the following meaning:
- dba_: All information contained objects database instance.
- v $ _: current instance of the dynamic view, and a management system comprising a system optimization view used.
- user_: Record object information of the user.
- gv_: Dynamic view of all instances of the distributed environment, comprising a view to optimize the use of systems and system management.
- all_: record the user's machine is authorized to access the object information of the object information.
Two, Oracle data dictionary used
1, the basic data dictionary
Basic data dictionary includes data storage logical storage structure and physical structure, additionally, further comprising tables that describe other data object information in the following table:
| Data Dictionary Name | Explanation |
| dba_tablespaces | Information about table spaces |
| dba_ts_quotas | All user table space quota |
| dba_free_space | All free partition table space |
| dba_segments | Description database storage of all segments |
| dba_extents | Database information for all partitions |
| dba_tables | Description of all the data tables in the database |
| dba_tab_columns | All tables, views and clusters of columns |
| dba_views | Database information for all views |
| dba_synonyms | Query information about synonyms |
| dba_sequences | Sequence information for all users |
| dba_constraints | All user information table constraints |
| dba_indexs | About database describing all indexes |
| dba_ind_columns | Compressed indexes on all tables and clusters column |
| dba_triggers | All users of the trigger information |
| dba_source | All user information stored procedure |
| dba_data_files | Query information about the database file |
| dba_tab_grants/privs | Query information about the object authorization |
| dba_objects | All objects in the database |
| dba_users | Information about the database for all users |
2, the dynamic performance views used
Internal Oracle system provides a large number of dynamic performance views, the reason that is "dynamic", because this information is constantly updated view of the database during operation. V $ dynamic performance views with the name prefix, these views provide information on the operation of memory and disk, read-only access users can not modify them. Following table:
| Data Dictionary Name | Explanation |
| v$database | Description information about the database |
| v$datafile | Data files used by the database information |
| v $ log | Extract information about redo log files from the control group |
| v$logfile | For information about instances reset the log file name and location of the group |
| v$archived_log | Basic information recording archive log files |
| v$archived_dest | Path information recorded archive log files |
| v$controlfile | Description of the control information file |
| v$instance | Basic example of the information recording |
| v$system_parameter | Examples of the display information currently valid parameter |
| v $ sga | Examples of the display size of the SGA area |
| v $ sgastat | Information SGA usage statistics |
| v$parameter | Record initialization parameter file values for all items |
| v$lock | By accessing the database session, set all the information object lock |
| v$session | For information about the session |
| v $ sqltext | Detailed records SQL statements |
| v $ sqltext | SQL statement recorded statement information |
| at $ bgprocess | Display background process information |
| v$process | Information about the current process |
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ocp exam:
Which two are true about the data dictionary?
A. Base tables in the data dictionary have the prefix DBA_.
B. All user actions are recorded in the data dictionary.
C. The data dictionary is constantly updated to reflect changes to database objects, permissions, and data.
D. All users have permissions to access all information in the data dictionary by default
E. The SYS user owns all base tables and user-accessible views in the data dictionary.
Correct Answer:CE
about dictionary？
1.The data dictionary is constantly updated to reflect changes to database objects, permissions, and data.
2.The SYS user owns all base tables and user-accessible views in the data dictionary.