Version sans cache

Mise en cache désactivé. Réglage défaut pour cette page : actif (code DEF204)
Si l'affichage est trop lent, vous pouvez désactiver le mode utilisateur pour visualiser la version en cache.

Rechercher dans le manuel MySQL

5.3 The mysql System Database

Table des matières

The mysql database is the system database. It contains tables that store information required by the MySQL server as it runs. A broad categorization is that the mysql database contains data dictionary tables that store database object metadata, and system tables used for other operational purposes. The following discussion further subdivides the set of system tables into smaller categories.

The remainder of this section enumerates the tables in each category, with cross references for additional information. Data dictionary tables and system tables use the InnoDB storage engine unless otherwise indicated.

mysql system tables and data dictionary tables reside in a single InnoDB tablespace file named mysql.ibd in the MySQL data directory. Previously, these tables were created in individual tablespace files in the mysql database directory.

Data Dictionary Tables

These tables comprise the data dictionary, which contains metadata about database objects. For additional information, see Chapter 14, MySQL Data Dictionary.

Important

The data dictionary is new in MySQL 8.0. A data dictionary-enabled server entails some general operational differences compared to previous MySQL releases. For details, see Section 14.7, “Data Dictionary Usage Differences”. Also, for upgrades to MySQL 8.0 from MySQL 5.7, the upgrade procedure differs somewhat from previous MySQL releases and requires that you verify the upgrade readiness of your installation by checking specific prerequisites. For more information, see Section 2.11.1, “Upgrading MySQL”, particularly Section 2.11.1.4, “Preparing Your Installation for Upgrade”.

  • catalogs: Catalog information.

  • character_sets: Information about available character sets.

  • collations: Information about collations for each character set.

  • column_statistics: Histogram statistics for column values. See Section 8.9.6, “Optimizer Statistics”.

  • column_type_elements: Information about types used by columns.

  • columns: Information about columns in tables.

  • dd_properties: A table that identifies data dictionary properties, such as its version. The server uses this to determine whether the data dictionary must be upgraded to a newer version.

  • events: Information about Event Scheduler events. See Section 24.4, “Using the Event Scheduler”. The server loads events listed in this table during its startup sequence, unless started with the --skip-grant-tables option.

  • foreign_keys, foreign_key_column_usage: Information about foreign keys.

  • index_column_usage: Information about columns used by indexes.

  • index_partitions: Information about partitions used by indexes.

  • index_stats: Used to store dynamic index statistics generated when ANALYZE TABLE is executed.

  • indexes: Information about table indexes.

  • innodb_ddl_log: Stores DDL logs for crash-safe DDL operations.

  • parameter_type_elements: Information about stored procedure and function parameters, and about return values for stored functions.

  • parameters: Information about stored procedures and functions. See Section 24.2, “Using Stored Routines (Procedures and Functions)”.

  • resource_groups: Information about resource groups. See Section 8.12.5, “Resource Groups”

  • routines: Information about stored procedures and functions. See Section 24.2, “Using Stored Routines (Procedures and Functions)”.

  • schemata: Information about schemata. In MySQL, a schema is a database, so this table provides information about databases.

  • st_spatial_reference_systems: Information about available spatial reference systems for spatial data.

  • table_partition_values: Information about values used by table partitions.

  • table_partitions: Information about partitions used by tables.

  • table_stats: Information about dynamic table statistics generated when ANALYZE TABLE is executed.

  • tables: Information about tables in databases.

  • tablespace_files: Information about files used by tablespaces.

  • tablespaces: Information about active tablespaces.

  • triggers: Information about triggers.

  • view_routine_usage: Information about dependencies between views and stored functions used by them.

  • view_table_usage: Used to track dependencies between views and their underlying tables.

Data dictionary tables are invisible. They cannot be read with SELECT, do not appear in the output of SHOW TABLES, are not listed in the INFORMATION_SCHEMA.TABLES table, and so forth. However, in most cases there are corresponding INFORMATION_SCHEMA tables that can be queried. Conceptually, the INFORMATION_SCHEMA provides a view through which MySQL exposes data dictionary metadata. For example, you cannot select from the mysql.schemata table directly:

  1. mysql> SELECT * FROM mysql.schemata;
  2. ERROR 3554 (HY000): Access to data dictionary table 'mysql.schemata' is rejected.

Instead, select that information from the corresponding INFORMATION_SCHEMA table:

  1. mysql> SELECT * FROM INFORMATION_SCHEMA.SCHEMATA\G
  2. *************************** 1. row ***************************
  3.               CATALOG_NAME: def
  4.                SCHEMA_NAME: mysql
  5. DEFAULT_CHARACTER_SET_NAME: utf8mb4
  6.     DEFAULT_COLLATION_NAME: utf8mb4_0900_ai_ci
  7.                   SQL_PATH: NULL
  8. *************************** 2. row ***************************
  9.               CATALOG_NAME: def
  10.                SCHEMA_NAME: information_schema
  11. DEFAULT_CHARACTER_SET_NAME: utf8
  12.     DEFAULT_COLLATION_NAME: utf8_general_ci
  13.                   SQL_PATH: NULL
  14. ...

There is no INFORMATION_SCHEMA table that corresponds exactly to mysql.indexes, but INFORMATION_SCHEMA.STATISTICS contains much of the same information.

As of yet, there are no INFORMATION_SCHEMA tables that correspond exactly to mysql.foreign_keys, mysql.foreign_key_column_usage. The standard SQL way to obtain foreign key information is by using the INFORMATION_SCHEMA REFERENTIAL_CONSTRAINTS and KEY_COLUMN_USAGE tables; these tables are now implemented as views on the foreign_keys, foreign_key_column_usage, and other data dictionary tables.

Some system tables from before MySQL 8.0 have been replaced by data dictionary tables and are no longer present in the mysql system database:

  • The events data dictionary table supersedes the event table from before MySQL 8.0.

  • The parameters and routines data dictionary tables together supersede the proc table from before MySQL 8.0.

Table des matières Haut

Grant System Tables

These system tables contain grant information about user accounts and the privileges held by them. For additional information about the structure, contents, and purpose of the these tables, see Section 6.2.3, “Grant Tables”.

As of MySQL 8.0, the grant tables are InnoDB (transactional) tables. Previously, these were MyISAM (nontransactional) tables. The change of grant-table storage engine underlies an accompanying change in MySQL 8.0 to the behavior of account-management statements such as CREATE USER and GRANT. Previously, an account-management statement that named multiple users could succeed for some users and fail for others. The statements are now transactional and either succeed for all named users or roll back and have no effect if any error occurs.

Note

If MySQL is upgraded from an older version but the grant tables have not been upgraded from MyISAM to InnoDB, the server considers them read only and account-management statements produce an error. For upgrade instructions, see Section 2.11.1, “Upgrading MySQL”.

  • user: User accounts, global privileges, and other non-privilege columns.

  • global_grants: Assignments of dynamic global privileges to users; see Section 6.2.2, “Static Versus Dynamic Privileges”.

  • db: Database-level privileges.

  • tables_priv: Table-level privileges.

  • columns_priv: Column-level privileges.

  • procs_priv: Stored procedure and function privileges.

  • proxies_priv: Proxy-user privileges.

  • default_roles: This table lists default roles to be activated after a user connects and authenticates, or executes SET ROLE DEFAULT.

  • role_edges: This table lists edges for role subgraphs.

    A given user table row might refer to a user account or a role. The server can distinquish whether a row represents a user account, a role, or both by consulting the role_edges table for information about relations between authentication IDs.

  • password_history: Information about password changes.

Table des matières Haut

Object Information System Tables

These system tables contain information about stored programs, components, user-defined functions, and server-side plugins:

Table des matières Haut

Log System Tables

The server uses these system tables for logging:

  • general_log: The general query log table.

  • slow_log: The slow query log table.

Log tables use the CSV storage engine.

For more information, see Section 5.4, “MySQL Server Logs”.

Table des matières Haut

Server-Side Help System Tables

These system tables contain server-side help information:

  • help_category: Information about help categories.

  • help_keyword: Keywords associated with help topics.

  • help_relation: Mappings between help keywords and topics.

  • help_topic: Help topic contents.

For more information, see Section 5.1.15, “Server-Side Help”.

Table des matières Haut

Time Zone System Tables

These system tables contain time zone information:

  • time_zone: Time zone IDs and whether they use leap seconds.

  • time_zone_leap_second: When leap seconds occur.

  • time_zone_name: Mappings between time zone IDs and names.

  • time_zone_transition, time_zone_transition_type: Time zone descriptions.

For more information, see Section 5.1.13, “MySQL Server Time Zone Support”.

Table des matières Haut

Replication System Tables

The server uses these system tables to support replication:

All of the tables just listed use the InnoDB storage engine.

Table des matières Haut

Optimizer System Tables

These system tables are for use by the optimizer:

Table des matières Haut

Miscellaneous System Tables

Other system tables do not fit the preceding categories:

  • audit_log_filter, audit_log_user: If MySQL Enterprise Audit is installed, these tables provide persistent storage of audit log filter definitions and user accounts. See Section 6.5.5.8.1, “Audit Log Tables”.

  • firewall_users, firewall_whitelist: If MySQL Enterprise Firewall is installed, these tables provide persistent storage for information used by the firewall. See Section 6.5.7, “MySQL Enterprise Firewall”.

  • servers: Used by the FEDERATED storage engine. See Section 16.8.2.2, “Creating a FEDERATED Table Using CREATE SERVER”.

  • innodb_dynamic_metadata: Used by the InnoDB storage engine to store fast-changing table metadata such as auto-increment counter values and index tree corruption flags. Replaces the data dictionary buffer table that resided in the InnoDB system tablespace.


Rechercher dans le manuel MySQL

Traduction non disponible

Le manuel MySQL n'est pas encore traduit en français sur l'infobrol. Seule la version anglaise est disponible pour l'instant.

Document créé le 26/06/2006, dernière modification le 26/10/2018
Source du document imprimé : https://www.gaudry.be/mysql-rf-system-database.html

L'infobrol est un site personnel dont le contenu n'engage que moi. Le texte est mis à disposition sous licence CreativeCommons(BY-NC-SA). Plus d'info sur les conditions d'utilisation et sur l'auteur.

Références

  1. Consulter le document html Langue du document :en Manuel MySQL : https://dev.mysql.com/

Ces références et liens indiquent des documents consultés lors de la rédaction de cette page, ou qui peuvent apporter un complément d'information, mais les auteurs de ces sources ne peuvent être tenus responsables du contenu de cette page.
L'auteur de ce site est seul responsable de la manière dont sont présentés ici les différents concepts, et des libertés qui sont prises avec les ouvrages de référence. N'oubliez pas que vous devez croiser les informations de sources multiples afin de diminuer les risques d'erreurs.

Table des matières Haut