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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

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
  • 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
  • table_cache_meta stores the metadata of cached tables.
  • 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
  • tidb_runaway_queries: the history records of all identified runaway queries in the past 7 days
  • tidb_runaway_quarantined_watch: the most recently active quick identification rules for runaway queries (contains currently valid rules, and possibly also contains recently expired rules)

Miscellaneous system tables

  • GLOBAL_VARIABLES: global system variable table
  • tidb: to record the version information when TiDB executes bootstrap
  • expr_pushdown_blacklist: the blocklist for expression pushdown
  • opt_rule_blacklist: the blocklist for logical optimization rules
  • table_cache_meta: the metadata of cached tables
  • tidb_import_jobs: the job information of IMPORT INTO
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