data dictionary
Data dictionary is the place where Oracle stores information about the internal database, which is used to describe the internal operation and management of the database. For example, the owner, creation time, table space, user access rights and other information of a data table can be found in the data dictionary. When users encounter difficulties in operating the database, they can provide help information by querying the data dictionary.
1. Introduction to Oracle data dictionary
Oracle The name of the data dictionary is composed of prefix and suffix, and the sliding line is used'_'The meaning of connection is as follows. a. dba_:Contains all object information of the database instance. b. v$_:The dynamic view of the current instance, including the views used by system management and system optimization. c. user_:Record the user's object information. d. gv_:Dynamic views of all instances in distributed environment, including views of system management and system optimization. e. all_:Record the object information that the user's object information machine is authorized to access.
2. Oracle common data dictionary
Although it is convenient to operate the database through Oracle Enterprise Manager (OEM), it is not conducive for readers to understand the internal structure of Oracle system and the relationship between application system objects. Therefore, it is recommended that readers try to use SQL*Plus to operate the database. In order to facilitate readers to understand the internal object structure of Oracle system and carry out high-level data management, the most commonly used data dictionary and its description are given below.
2.1 basic data dictionary
The basic data dictionary mainly includes data tables describing logical storage structure and physical storage structure. In addition, it also includes tables describing other data object information, such as dba_views, dba_triggers, dba_users et al. The basic data dictionary and its description are shown in the table below:
Basic data dictionary and its description ---------------------------------------------------------------- Data dictionary name explain ---------------------------------------------------------------- dba_tablespaces Information about tablespaces dba_ts_quotas Table space quota for all users dba_free_space Free partitions in all tablespaces dba_segments Describes the storage space of all segments in the database dba_extents All partition information in the database dba_tables Description of all data tables in the database dba_tab_columns Columns of all tables, views and clusters dba_views Information about all views in the database dba_synonyms Information query about synonyms dba_sequences All user sequence information dba_constrains Constraint information for all user tables dba_indexs Description of all indexes in the database dba_ind_columns Compress indexed columns on all tables and clusters dba_triggers Trigger information for all users dba_source Stored procedure information for all users dba_data_files Query information about database files dba_tab_grants/privs Query information about object authorization dba_objects All objects in the database dba_users Information about all users in the database ----------------------------------------------------------------
2.2 common dynamic performance views
Oracle system provides a large number of dynamic performance views. The reason why we say "dynamic" is that the information of these views will be constantly updated during the operation of the database. Dynamic performance views are prefixed with v $. These views provide information about the operation of memory and disk. Users can only access them read-only and cannot modify them. Common dynamic performance views and their descriptions are shown in the table below:
Common dynamic performance views ---------------------------------------------------------------- Data dictionary name explain ---------------------------------------------------------------- v$database Describes information about the database v$datafile Data file information used by the database v$log Extract information about redo log groups from the control file v$logfile Information about the instance reset log group file name and its location v$archived_log Record archive log file·Basic information of v$archived_dest Record the path information of the archive log file v$controlfile Describe the relevant information of the control document v$instance Record the basic information of the instance v$system_parameter Displays the currently valid parameter information of the instance v$sga Displays the of the instance SGA Size of v$sgastat Statistics SGA Information on usage v$parameter Record the values of all items in the initialization parameter file v$lock Set all the information of the object lock by accessing the database session v$session Information about the session v$sql record SQL Statement details v$sqltext record SQL Statement information of the statement v$bgprocess Display background process information v$process Information about the current process
The above introduces the basic contents of Oracle data dictionary. In fact, the contents of Oracle data dictionary are very rich. Due to the limited space, we can't list them one by one. Readers need to accumulate gradually in their study and work. The use of data dictionary technology can enable users to better understand the overall picture of the database, which is of great help to database optimization and management.
Oracle data dictionary is an evolving and changing internal table.