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DM-worker Introduction

DM-worker is a tool used to migrate data from MySQL/MariaDB to TiDB.

It has the following features:

  • Acts as a secondary database of any MySQL or MariaDB instance
  • Reads the binlog events from MySQL/MariaDB and persists them to the local storage
  • A single DM-worker supports migrating the data of one MySQL/MariaDB instance to multiple TiDB instances
  • Multiple DM-workers support migrating the data of multiple MySQL/MariaDB instances to one TiDB instance

DM-worker processing unit

A DM-worker task contains multiple logic units, including relay log, Dumper, Loader, and binlog replication.

Relay log

The relay log persistently stores the binlog data from the upstream MySQL/MariaDB and provides the feature of accessing binlog events for the binlog replication.

Its rationale and features are similar to the relay log of MySQL. For details, see MySQL Relay Log.

Dumper

Dumper dumps the full data from the upstream MySQL/MariaDB to the local disk.

Loader

Loader reads the files of Dumper and then loads these files to the downstream TiDB.

Binlog replication/Syncer

Binlog replication/Syncer reads the binlog events of the upstream MySQL/MariaDB or the binlog events of the relay log, transforms these events to SQL statements, and then applies these statements to the downstream TiDB.

Privileges required by DM-worker

This section describes the upstream and downstream database users' privileges required by DM-worker, and the user privileges required by the respective processing unit.

Upstream database user privileges

The upstream database (MySQL/MariaDB) user must have the following privileges:

PrivilegeScope
SELECTTables
RELOADGlobal
REPLICATION SLAVEGlobal
REPLICATION CLIENTGlobal

If you need to migrate the data from db1 to TiDB, execute the following GRANT statement:

GRANT RELOAD,REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'your_user'@'your_wildcard_of_host'
GRANT SELECT ON db1.* TO 'your_user'@'your_wildcard_of_host';

If you also need to migrate the data from other databases into TiDB, make sure the same privileges are granted to the user of the respective databases.

Downstream database user privileges

The downstream database (TiDB) user must have the following privileges:

PrivilegeScope
SELECTTables
INSERTTables
UPDATETables
DELETETables
CREATEDatabases, tables
DROPDatabases, tables
ALTERTables
INDEXTables

Execute the following GRANT statement for the databases or tables that you need to migrate:

GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP,ALTER,INDEX  ON db.table TO 'your_user'@'your_wildcard_of_host';

Minimal privilege required by each processing unit

Processing unitMinimal upstream (MySQL/MariaDB) privilegeMinimal downstream (TiDB) privilegeMinimal system privilege
Relay logREPLICATION SLAVE (reads the binlog)
REPLICATION CLIENT (show master status, show slave status)
NULLRead/Write local files
DumperSELECT
RELOAD (flushes tables with Read lock and unlocks tables)
NULLWrite local files
LoaderNULLSELECT (Query the checkpoint history)
CREATE (creates a database/table)
DELETE (deletes checkpoint)
INSERT (Inserts the Dump data)
Read/Write local files
Binlog replicationREPLICATION SLAVE (reads the binlog)
REPLICATION CLIENT (show master status, show slave status)
SELECT (shows the index and column)
INSERT (DML)
UPDATE (DML)
DELETE (DML)
CREATE (creates a database/table)
DROP (drops databases/tables)
ALTER (alters a table)
INDEX (creates/drops an index)
Read/Write local files

Note:

These privileges are not immutable and they change as the request changes.