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TiDB Data Migration Block and Allow Lists
Learn how to use the DM block and allow lists feature.

TiDB Data Migration Block and Allow Lists

When you migrate data using TiDB Data Migration (DM), you can configure the block and allow lists to filter or only migrate all operations of some databases or some tables.

Configure the block and allow lists

In the task configuration file, add the following configuration:

block-allow-list:             # Use black-white-list if the DM version is earlier than or equal to v2.0.0-beta.2.
  rule-1:
    do-dbs: ["test*"]         # Starting with characters other than "~" indicates that it is a wildcard;
                              # v1.0.5 or later versions support the regular expression rules.
    do-tables:
    - db-name: "test[123]"    # Matches test1, test2, and test3.
      tbl-name: "t[1-5]"      # Matches t1, t2, t3, t4, and t5.
    - db-name: "test"
      tbl-name: "t"
  rule-2:
    do-dbs: ["~^test.*"]      # Starting with "~" indicates that it is a regular expression.
    ignore-dbs: ["mysql"]
    do-tables:
    - db-name: "~^test.*"
      tbl-name: "~^t.*"
    - db-name: "test"
      tbl-name: "t*"
    ignore-tables:
    - db-name: "test"
      tbl-name: "log"

In simple scenarios, it is recommended that you use the wildcard for matching schemas and tables. However, note the following version differences:

  • Wildcards including *, ?, and [] are supported. There can only be one * symbol in a wildcard match, and it must be at the end. For example, in tbl-name: "t*", "t*" indicates all tables starting with t. See wildcard matching for details.

  • A regular expression must begin with the ~ character.

Parameter descriptions

  • do-dbs: allow lists of the schemas to be migrated, similar to replicate-do-db in MySQL.
  • ignore-dbs: block lists of the schemas to be migrated, similar to replicate-ignore-db in MySQL.
  • do-tables: allow lists of the tables to be migrated, similar to replicate-do-table in MySQL. Both db-name and tbl-name must be specified.
  • ignore-tables: block lists of the tables to be migrated, similar to replicate-ignore-table in MySQL. Both db-name and tbl-name must be specified.

If a value of the above parameters starts with the ~ character, the subsequent characters of this value are treated as a regular expression. You can use this parameter to match schema or table names.

Filtering process

Note:

In DM and in MySQL, the block and allow lists filtering rules are different in the following ways:

  • In MySQL, replicate-wild-do-table and replicate-wild-ignore-table support wildcard characters. In DM, some parameter values directly supports regular expressions that start with the ~ character.
  • DM currently only supports binlogs in the ROW format, and does not support those in the STATEMENT or MIXED format. Therefore, the filtering rules in DM correspond to those in the ROW format in MySQL.
  • MySQL determines a DDL statement only by the database name explicitly specified in the USE section of the statement. DM determines a statement first based on the database name section in the DDL statement. If the DDL statement does not contain such a section, DM determines the statement by the USE section. Suppose that the SQL statement to be determined is USE test_db_2; CREATE TABLE test_db_1.test_table (c1 INT PRIMARY KEY); that replicate-do-db=test_db_1 is configured in MySQL and do-dbs: ["test_db_1"] is configured in DM. Then this rule only applies to DM and not to MySQL.

The filtering process of a test.t table is as follows:

  1. Filter at the schema level:

    • If do-dbs is not empty, check whether a matched schema exists in do-dbs.

      • If yes, continue to filter at the table level.
      • If not, filter test.t.

    • If do-dbs is empty and ignore-dbs is not empty, check whether a matched schema exits in ignore-dbs.

      • If yes, filter test.t.
      • If not, continue to filter at the table level.

    • If both do-dbs and ignore-dbs are empty, continue to filter at the table level.

  2. Filter at the table level:

    1. If do-tables is not empty, check whether a matched table exists in do-tables.

      • If yes, migrate test.t.
      • If not, filter test.t.

    2. If ignore-tables is not empty, check whether a matched table exists in ignore-tables.

      • If yes, filter test.t.
      • If not, migrate test.t.

    3. If both do-tables and ignore-tables are empty, migrate test.t.

Note:

To check whether the schema test should be filtered, you only need to filter at the schema level.

Usage examples

Assume that the upstream MySQL instances include the following tables:

`logs`.`messages_2016`
`logs`.`messages_2017`
`logs`.`messages_2018`
`forum`.`users`
`forum`.`messages`
`forum_backup_2016`.`messages`
`forum_backup_2017`.`messages`
`forum_backup_2018`.`messages`

The configuration is as follows:

block-allow-list:  # Use black-white-list if the DM version is earlier than or equal to v2.0.0-beta.2.
  bw-rule:
    do-dbs: ["forum_backup_2018", "forum"]
    ignore-dbs: ["~^forum_backup_"]
    do-tables:
    - db-name: "logs"
      tbl-name: "~_2018$"
    - db-name: "~^forum.*"
​      tbl-name: "messages"
    ignore-tables:
    - db-name: "~.*"
​      tbl-name: "^messages.*"

After applying the bw-rule rule:

Table Whether to filter Why filter
logs.messages_2016 Yes The schema logs fails to match any do-dbs.
logs.messages_2017 Yes The schema logs fails to match any do-dbs.
logs.messages_2018 Yes The schema logs fails to match any do-dbs.
forum_backup_2016.messages Yes The schema forum_backup_2016 fails to match any do-dbs.
forum_backup_2017.messages Yes The schema forum_backup_2017 fails to match any do-dbs.
forum.users Yes 1. The schema forum matches do-dbs and continues to filter at the table level.
2. The schema and table fail to match any of do-tables and ignore-tables and do-tables is not empty.
forum.messages No 1. The schema forum matches do-dbs and continues to filter at the table level.
2. The table messages is in the db-name: "~^forum.*",tbl-name: "messages" of do-tables.
forum_backup_2018.messages No 1. The schema forum_backup_2018 matches do-dbs and continues to filter at the table level.
2. The schema and table match the db-name: "~^forum.*",tbl-name: "messages" of do-tables.