Oracle advanced (III) detailed explanation of data dictionary

One 、Oracle The data dictionary

The data dictionary is

Oracle

A place for storing information about a database , Its purpose is to describe data . For example, the creator information of a table , Create time information , Table space information , User access information, etc . When users encounter difficulties in operating the data in the database, they can access the data dictionary to view the detailed information .　　

Oracle

There are static and dynamic data dictionaries in . The static data dictionary will not change when users access the data dictionary , But dynamic data dictionary depends on database performance , Reflect some internal information of database operation , Therefore, when accessing this kind of data dictionary, it is often not invariable . These two types of data dictionaries are discussed below .

1.1  Static data dictionary

This kind of data dictionary is mainly composed of tables and views , It should be noted that , Tables in the data dictionary cannot be accessed directly , But you can access the views in the data dictionary . Views in the static data dictionary fall into three categories , They are respectively composed of three prefixes ：

user_*

、 

all_*

、 

dba_*

.

• user_*
   : This view stores information about the objects owned by the current user .（ That is, all objects in the user mode ）

• all_*
  :  This attempt stores information about objects that the current user can access .（ And
  user_*
  comparison ,
  all_*
    You don't need to own the object , You just need to have access to the object ）

• dba_*
  :  This view stores information about all objects in the database .（ The premise is that the current user has access to these databases , Generally speaking, you must have administrator rights ）

As can be seen from the above description , The data stored between the three will definitely overlap , In fact, in addition to the different access ranges （ Because the permissions are different , So the scope of access objects is different ）, Others are consistent . say concretely , Because the data dictionary view is made up of

SYS

（ System users ） Owned , So by default , Only SYS And have DBA Users with system permissions can see all views . No, DBA Users with permissions can only see

user_*

and

all_*

View . If not granted relevant

SELECT

permissions , They can't see  

dba_*

View's .

Because the three have similarities , Let's say

user_

As an example, this paper introduces several commonly used static views

• user_users
  View ： It mainly describes the information of the current user , It mainly includes the current user name 、 account id、 Account status 、 Table space name 、 Creation time, etc . For example, execute the following command to return this information .

select * from user_users


• user_tables
  View ： It mainly describes the information of all tables owned by the current user , It mainly includes table name 、 Table space name 、 Cluster name, etc . Through this view, you can clearly understand which tables the current user can operate . The execution order is ：
  select * from user_tables

• user_objects
  View ： It mainly describes the information of all objects owned by the current user , Objects include tables 、 View 、 stored procedure 、 trigger 、 package 、 Indexes 、 Sequence, etc . This view is better than
  user_tables
  The view is more comprehensive . for example ,  You need to get a file named “package1” Information about the object type and its state , You can execute the following command ：
  select object_type,status from user_objects where object_name=upper(‘package1’);

Be careful ：upper Use , All objects in the data dictionary are capitalized , and PL/SQL It's not case sensitive , So in practice, we must pay attention to case matching .

• user_tab_privs
  View ： This view mainly stores the permission information of all tables under the current user . such as , In order to understand the current user's response to table1 Permission information of , You can execute the following command ：

select * from user_tab_privs where table_name=upper('table1')


After knowing the permissions of the current user on this table, you can clearly know , What operations can be performed , Which operations cannot be performed .

The front views are user_ At the beginning , Actually all_ The beginning is exactly the same , Only the listed information is the object that the current user can access, not the object owned by the current user . about dba_ The first one needs administrator permission , Other uses are exactly the same , I won't go into that here .

1.2  Dynamic data dictionary

Oracle Contains a number of potential applications by system administrators such as SYS Maintained tables and views , Because when databases are running, they are constantly updated , So we call them dynamic data dictionaries （ Or dynamic performance view ）. These views provide information about the operation of memory and disk , So we can only access them read-only, not modify them .

Oracle These dynamic performance views are based on

v$

The first view , such as

v$access

. Here are some main dynamic performance views .

• v$access
  ： This view shows the database objects locked in the database and the session objects accessing these objects （session object ）.

Run the following command ：

select * from v$access


give the result as follows ：（ Because there are many records , So here is only an excerpt of some records ）

SID
OWNER OBJECT TYPE
27 DKH V$ACCESS CURSOR
27 PUBLIC V$ACCESS SYNONYM
27 SYS DBMS_APPLICATION_INFO PACKAGE
27 SYS GV$ACCESS VIEW


• v$session
  ： This view lists the details of the current session . Because there are many fields in this view , No detailed fields are listed here , For more information , Can be directly in sql*plus Type... At the command line ：
  desc v$session
  that will do .

• v$active_instance
  ： This view mainly describes the information of the active instances under the current database . Still usable select Statement to observe the information .

• v$context
  ： This view lists the attribute information of the current session . For example, the namespace 、 Property value, etc .

1.3  Summary

Above is Oracle The basic content of data dictionary , There are also many useful views that cannot be explained here because of space , I hope you will pay more attention to it in your daily use . All in all , Make good use of data dictionary technology , It can enable database developers to better understand the overall picture of the database , So for database optimization 、 Management is of great help .

Two 、Oracle  Data dictionary commonly used in

These data dictionaries are listed below , Both in  Oracle 11g R1  On , adopt  Oracle Sql Developer  Tested , All pass . Many of these data dictionaries must be  system  Or is it  sysdba  Users can only use it after logging in .

--- Basic information of database instances  
desc v$instance; 
select * from v$instance;

-- Basic information of data file  
desc v$datafile; 
select * from v$datafile; 
desc dba_data_files; 
select file_name,file_id,tablespace_name,bytes,blocks, tatus,online_status from dba_data_files;

-- Basic information of temporary files  
desc dba_temp_files; 
select file_name,file_id,tablespace_name,status, from dba_temp_files;

-- Basic information of control document  
desc v$controlfile; 
select name,status,is_recovery_dest_file, block_size,file_size_blks from v$controlfile;

-- Basic information of log file  
desc v$logfile; 
select group#,status,type,member,is_recovery_dest_file from v$logfile;