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Precheck the Upstream MySQL Instance Configurations

This document introduces the precheck feature provided by DM. This feature is used to detect possible errors in the upstream MySQL instance configuration when the data migration task is started.

Command

check-task allows you to precheck whether the upstream MySQL instance configuration satisfies the DM requirements.

Checking items

Upstream and downstream database users must have the corresponding read and write privileges. DM checks the following privileges and configuration automatically while the data migration task is started:

  • Database version

    • 5.5 < MySQL version < 8.0
    • MariaDB version >= 10.1.2
  • MySQL binlog configuration

    • Whether the binlog is enabled (DM requires that the binlog must be enabled)
    • Whether binlog_format=ROW (DM only supports migration of the binlog in the ROW format)
    • Whether binlog_row_image=FULL (DM only supports binlog_row_image=FULL)
  • The privileges of the upstream MySQL instance users

    MySQL users in DM configuration need to have the following privileges at least:

    • REPLICATION SLAVE
    • REPLICATION CLIENT
    • RELOAD
    • SELECT
  • The compatibility of the upstream MySQL table schema

    TiDB differs from MySQL in compatibility in the following aspects:

    • TiDB does not support the foreign key.

    • Character set compatibility differs.

      DM will also check whether the primary key or unique key restriction exists in all upstream tables. This check is introduced in v1.0.7.

  • The consistency of the sharded tables in the multiple upstream MySQL instances

    • The schema consistency of all sharded tables

      • Column size
      • Column name
      • Column position
      • Column type
      • Primary key
      • Unique index
    • The conflict of the auto increment primary keys in the sharded tables

      • The check fails in the following two conditions:

        • The auto increment primary key exists in the sharded tables and its column type is not bigint.
        • The auto increment primary key exists in the sharded tables and its column type is bigint, but column mapping is not configured.
      • The check succeeds in other conditions except the two above.

Disable checking items

DM checks items according to the task type, and you can use ignore-checking-items in the task configuration file to disable checking items. The list of element options for ignore-checking-items is as follows:

ElementDescription
allDisables all checks
dump_privilegeDisables checking dump-related privileges of the upstream MySQL instance user
replication_privilegeDisables checking replication-related privileges of the upstream MySQL instance user
versionDisables checking the upstream database version
binlog_enableDisables checking whether the upstream database has binlog enabled
binlog_formatDisables checking whether the binlog format of the upstream database is ROW
binlog_row_imageDisables checking whether the binlog_row_image of the upstream database is FULL
table_schemaDisables checking the compatibility of the upstream MySQL table schema
schema_of_shard_tablesDisables checking whether the schemas of upstream MySQL sharded tables are consistent in the multi-instance sharding scenario
auto_increment_IDDisables checking the conflicts of auto-increment primary keys of the upstream MySQL shared tables in the multi-instance sharding scenario