Dynamic performance view overview

Overview of dynamic performance view

The dynamic performance view belongs to the data dictionary , They are owned by SYS, And most dynamic performance views can only be accessed by privileged users and DBA User query .

When the database is in a different state , The dynamic performance views available are different .

When starting a routine ,ORACLE Dynamic performance views are automatically created ; When stopping a routine ,ORACLE The dynamic performance view is automatically deleted .

Data dictionary information is obtained from data files , The dynamic performance view information is from SGA And control documents .

therefore , There is a big difference between the two . Database administrators take advantage of these dynamic performance views , You can learn some basic information about database operation , Provide some data support for our database maintenance and database performance optimization .
 

The dynamic performance view is constantly updated as the database is opened and used , And their content is mainly about performance .

Although these views are much like ordinary database tables , But they don't allow users to make changes directly .

These views provide data about the internal disk structure and memory structure . Users can query these views , In order to manage and optimize the system .

All dynamic performance views are based on V_$ At the beginning ,ORACLE Synonyms are provided for each dynamic performance view （V$ start ）. V$ yes V_$ A synonym for .

By inquiring V$FIXED_TABLE, All dynamic performance views can be displayed .
Dynamic performance view of database in different states
 

In general , We can master two kinds of important database operation information through dynamic performance data .

    Understand the performance data related to database operation , Such as memory usage 、 Sort the disks The probability of birth and so on .
    Get other information about disk and memory structure .

In general , The dynamic performance views of different database states are quite different ：
NOMOUNT

When starting a routine ,ORACLE Will open the parameter file , Distribute SGA And start the background process . So the routine is in NOMOUNT In the state of , Can only access from SGA Dynamic performance view to get information from .

SGA----V$PARAMETER     V$SGA   V$OPTION V$PROCESS
       V$SESSION        V$VERSION V$INSTANCE

MOUNT

When loading the database ,ORACLE According to the initialization parameters control_file Open all control files . When the routine is in MOUNT In the state of , Not only can you access SGA Dynamic performance view to get information from , You can also access the dynamic performance view that gets information from the control file .

Control documents -------V$THREAD V$CONTROLFILE V$DATABASE
            V$DATAFILE   V$DATAFILE_HEADER   V$LOGFILE
 

OPEN

When the database is open ,ORACLE Open all data files and redo logs according to the information recorded in the control file . In addition to being able to access SGA And control files to get information from the dynamic performance view , You can also visit ORACLE Performance related dynamic performance view （V$FILESTAT V$SESSION_WAIT V$WAITSTAT）

Pay attention to is , Only in OPEN In the state of , To access the data dictionary view .
V$, V_$, GV$, X$
X$ surface

X$ The table contains information about all aspects of a particular instance , yes Oracle Operation basis of database , Such as the current configuration information , The session connected to the instance , And rich and valuable performance information .
 

X$ Tables are not permanent or temporary tables that reside in database files . X$ Tables only reside in memory , When the instance starts , from Oracle Application dynamic creation , Real time maintenance in memory .

Most of them need at least databases that are loaded or already open .

X$ The table is SYS What the user owns , And it's read-only . Cannot be DML( to update , Insert , Delete ). Tables are critical to a database , therefore Oracle Don't allow SYSDBA Direct access to , Display authorization not allowed .

About X$ surface , We can also create information through bootstrap$ Table view , This table records the basic and driver information of database startup .

bootstrap$ What is actually stored is the definition of the base table of the data dictionary , Such as OBJ$,C_OBJ$,TAB$ wait .

Oracle Create the base table of the data dictionary by reading these definitions , And then create a data dictionary .

The query must be sys user ,dba The user with permission has no permission to query .
 

GV$ and V$ A synonym for
V$ View

The dynamic performance view is prefixed by V_$ identification . The common synonyms for these views have prefixes V$. data
Library administrators or users should only access V$ object , Instead of visiting V_$ object .

Once the instance starts , Read data from memory V$ The view is accessible .

Be careful : Every V$ Views contain similar statements ：

where inst_id = USERENV('Instance')

Used to restrict the return of current instance information .

We can do this through V$FIXED_VIEW_DEFINITION View To verify

select view_definition from v_$fixed_view_definition where
view_name='V$FIXED_TABLE';

You have to use sys User query .

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