System Tables

After initialization, an instance contains several system databases that store metadata, compatibility-layer information, and internal runtime data. System objects are read-only by default. Do not write business logic that modifies undocumented internal table structures.

System databases

Database

Product-oriented purpose

mo_catalog

MatrixOne metadata, including databases, tables, columns, indexes, users, roles, and grant relationships

information_schema

Information-schema views compatible with common table-structure and privilege inspection workflows

mysql

A subset of system tables for the MySQL compatibility layer

system

Runtime and log system data

system_metrics

System metrics data

Some older documents use a spelling variant for the metrics database. Refer to the actual database name returned by SHOW DATABASES; the common name is system_metrics.

Common mo_catalog tables

You do not need to memorize every column. Query the tables required for the task:

Table

What it contains

mo_database

Database list, creation information, subscription status, and more

Table and column metadata tables

Table and column definitions. Exact names depend on the instance, such as the mo_tables / mo_columns family.

mo_indexes

Index ID, type (primary, unique, or secondary), algorithm, and component columns

mo_table_partitions

Partition definitions. RANGE/LIST and other types may be unsupported. See Limitations.

mo_user

User name, status, creation time, default role, and more

mo_role

Roles

mo_user_grant

Roles granted to users

mo_role_grant

Role inheritance

mo_role_privs

Privilege details for roles

User-defined-function tables

User-defined function metadata

 
-- Example: view metadata for currently visible databases (requires the appropriate privileges)
SELECT datname, dat_type, created_time
FROM mo_catalog.mo_database
LIMIT 20;

information_schema and mysql

  • For tool compatibility with information_schema.tables, columns, schemata, and similar objects, prefer this layer.

  • Compatibility is a subset. Some MySQL system tables or columns do not exist or always remain empty. Do not assume 100% compatibility with MySQL 8.0.

Usage notes

  1. Read-only: DML or DDL on system databases is generally rejected or can cause unexpected behavior.

  2. Privileges: Ordinary business roles may not see all system tables. Administrative roles have broader visibility.

  3. Version differences: Internal table columns evolve between versions. Automation should tolerate added columns and avoid depending on the column order returned by SELECT *.

  4. Cleanup: Dedicated functions such as PURGE_LOG may be available for log cleanup. Do not modify underlying files or tables directly.