mysql Schema

The mysql schema contains TiDB system tables. The design is similar to the mysql schema in MySQL, where tables such as mysql.user can be edited directly. It also contains a number of tables which are extensions to MySQL.

Grant system tables

These system tables contain grant information about user accounts and their privileges:

• user: user accounts, global privileges, and other non-privilege columns
• db: database-level privileges
• tables_priv: table-level privileges
• columns_priv: column-level privileges
• password_history: password change history
• default_roles: the default roles for a user
• global_grants: dynamic privileges
• global_priv: the authentication information based on certificates
• role_edges: the relationship between roles

Cluster status system tables

• The tidb table contains some global information about TiDB:

  • bootstrapped: whether the TiDB cluster has been initialized. Note that this value is read-only and cannot be modified.
  • tidb_server_version: the version information of TiDB when it is initialized. Note that this value is read-only and cannot be modified.
  • system_tz: the system time zone of TiDB.
  • new_collation_enabled: whether TiDB has enabled the new framework for collations. Note that this value is read-only and cannot be modified.

Server-side help system tables

Currently, the help_topic is NULL.

Statistics system tables

• stats_buckets: the buckets of statistics
• stats_histograms: the histograms of statistics
• stats_top_n: the TopN of statistics
• stats_meta: the meta information of tables, such as the total number of rows and updated rows
• stats_extended: extended statistics, such as the order correlation between columns
• stats_feedback: the query feedback of statistics
• stats_fm_sketch: the FMSketch distribution of the histogram of the statistics column
• analyze_options: the default analyze options for each table
• column_stats_usage: the usage of column statistics
• schema_index_usage: the usage of indexes
• analyze_jobs: the ongoing statistics collection tasks and the history task records within the last 7 days

Execution plan-related system tables

• bind_info: the binding information of execution plans
• capture_plan_baselines_blacklist: the blocklist for the automatic binding of the execution plan

GC worker system tables

• gc_delete_range: the KV range to be deleted
• gc_delete_range_done: the deleted KV range

System tables related to cached tables

• table_cache_meta stores the metadata of cached tables.

TTL related system tables

The TTL related system tables are not available on TiDB Serverless clusters.

• tidb_ttl_table_status: the previously executed TTL job and ongoing TTL job for all TTL tables
• tidb_ttl_task: the current ongoing TTL subtasks
• tidb_ttl_job_history: the execution history of TTL tasks in the last 90 days

System tables related to runaway queries

• tidb_runaway_queries: the history records of all identified runaway queries in the past 7 days
• tidb_runaway_watch: the watch list of runaway queries
• tidb_runaway_watch_done: a watch list of deleted or expired runaway queries

System tables related to metadata locks

• tidb_mdl_view: a view of metadata locks. You can use it to view information about the currently blocked DDL statements
• tidb_mdl_info: used internally by TiDB to synchronize metadata locks across nodes

System tables related to DDL statements

• tidb_ddl_history: the history records of DDL statements
• tidb_ddl_jobs: the metadata of DDL statements that are currently being executed by TiDB
• tidb_ddl_reorg: the metadata of physical DDL statements (such as adding indexes) that are currently being executed by TiDB

System tables related to TiDB Distributed eXecution Framework (DXF)

• dist_framework_meta: the metadata of the Distributed eXecution Framework (DXF) task scheduler
• tidb_global_task: the metadata of the current DXF task
• tidb_global_task_history: the metadata of the historical DXF tasks, including both succeeded and failed tasks
• tidb_background_subtask: the metadata of the current DXF subtask
• tidb_background_subtask_history: the metadata of the historical DXF subtasks

Miscellaneous system tables

• GLOBAL_VARIABLES: global system variable table
• expr_pushdown_blacklist: the blocklist for expression pushdown
• opt_rule_blacklist: the blocklist for logical optimization rules
• tidb_import_jobs: the job information of IMPORT INTO
• tidb_timers: the metadata of internal timers