Data Migration Shard Merge Scenario

This document shows how to use Data Migration (DM) in the shard merge scenario where the sharded schemas and sharded tables data of three upstream MySQL instances need to be replicated to a downstream TiDB cluster.

Upstream instances

Assume that the upstream schemas are as follows:

• Instance 1

  Schema	Tables
  user	information, log_north, log_bak
  store_01	sale_01, sale_02
  store_02	sale_01, sale_02

• Instance 2

  Schema	Tables
  user	information, log_east, log_bak
  store_01	sale_01, sale_02
  store_02	sale_01, sale_02

• Instance 3

  Schema	Tables
  user	information, log_south, log_bak
  store_01	sale_01, sale_02
  store_02	sale_01, sale_02

Replication requirements

1. Merge the user.information table of three upstream instances to the downstream user.information table in TiDB.
2. Merge the user.log_{north|south|east} table of three upstream instances to the downstream user.log_{north|south|east} table in TiDB.
3. Merge the store_{01|02}.sale_{01|02} table of three upstream instances to the downstream store.sale table in TiDB.
4. Filter out all the deletion operations in the user.log_{north|south|east} table of three upstream instances.
5. Filter out all the deletion operations in the user.information table of three upstream instances.
6. Filter out all the deletion operations in the store_{01|02}.sale_{01|02} table of three upstream instances.
7. Filter out the user.log_bak table of three upstream instances.
8. Because the store_{01|02}.sale_{01|02} tables have auto-increment primary keys of the bigint type, the conflict occurs when these tables are merged into TiDB. The following text will show you solutions to resolve and avoid the conflict.

Downstream instances

Assume that the downstream schema after replication is as follows:

Replication solution

• To satisfy the replication Requirements #1 and #2, configure the table routing rule as follows:

  routes:
    ...
    user-route-rule:
      schema-pattern: "user"
      target-schema: "user"

• To satisfy the replication Requirement #3, configure the table routing rule as follows:

  routes:
    ...
    store-route-rule:
      schema-pattern: "store_*"
      target-schema: "store"
    sale-route-rule:
      schema-pattern: "store_*"
      table-pattern: "sale_*"
      target-schema: "store"
      target-table:  "sale"

• To satisfy the replication Requirements #4 and #5, configure the binlog event filtering rule as follows:

  filters:
    ...
    user-filter-rule:
      schema-pattern: "user"
      events: ["truncate table", "drop table", "delete", "drop database"]
      action: Ignore

  Note:

  The replication Requirements #4, #5 and #7 indicate that all the deletion operations in the user schema are filtered out, so a schema level filtering rule is configured here. However, the deletion operations of future tables in the user schema will also be filtered out.

• To satisfy the replication Requirement #6, configure the binlog event filter rule as follows:

  filters:
    ...
    sale-filter-rule:
      schema-pattern: "store_*"
      table-pattern: "sale_*"
      events: ["truncate table", "drop table", "delete"]
      action: Ignore
    store-filter-rule:
      schema-pattern: "store_*"
      events: ["drop database"]
      action: Ignore

• To satisfy the replication Requirement #7, configure the black and white table lists as follows:

  black-white-list:
    log-bak-ignored:
      ignore-tales:
      - db-name: "user"
        tbl-name: "log_bak"

• To satisfy the replication Requirement #8, first refer to handling conflicts of auto-increment primary key to solve conflicts. This guarantees that data is successfully replicated to the downstream when the primary key value of one sharded table is duplicate with that of another sharded table. Then, configure ignore-checking-items to skip checking the conflict of auto-increment primary key:

  ignore-checking-items: ["auto_increment_ID"]

Replication task configuration

The complete configuration of the replication task is shown as below. For more details, see Data Migration Task Configuration File.

name: "shard_merge"
task-mode: all
meta-schema: "dm_meta"
remove-meta: false
ignore-checking-items: ["auto_increment_ID"]

target-database:
  host: "192.168.0.1"
  port: 4000
  user: "root"
  password: ""

mysql-instances:
  -
    source-id: "instance-1"
    route-rules: ["user-route-rule", "store-route-rule", "sale-route-rule"]
    filter-rules: ["user-filter-rule", "store-filter-rule" , "sale-filter-rule"]
    black-white-list:  "log-bak-ignored"
    mydumper-config-name: "global"
    loader-config-name: "global"
    syncer-config-name: "global"

  -
    source-id: "instance-2"
    route-rules: ["user-route-rule", "store-route-rule", "sale-route-rule"]
    filter-rules: ["user-filter-rule", "store-filter-rule" , "sale-filter-rule"]
    black-white-list:  "log-bak-ignored"
    mydumper-config-name: "global"
    loader-config-name: "global"
    syncer-config-name: "global"
  -
    source-id: "instance-3"
    route-rules: ["user-route-rule", "store-route-rule", "sale-route-rule"]
    filter-rules: ["user-filter-rule", "store-filter-rule" , "sale-filter-rule"]
    black-white-list:  "log-bak-ignored"
    mydumper-config-name: "global"
    loader-config-name: "global"
    syncer-config-name: "global"

# Other common configs shared by all instances.

routes:
  user-route-rule:
    schema-pattern: "user"
    target-schema: "user"
  store-route-rule:
    schema-pattern: "store_*"
    target-schema: "store"
  sale-route-rule:
    schema-pattern: "store_*"
    table-pattern: "sale_*"
    target-schema: "store"
    target-table:  "sale"

filters:
  user-filter-rule:
    schema-pattern: "user"
    events: ["truncate table", "drop table", "delete", "drop database"]
    action: Ignore
  sale-filter-rule:
    schema-pattern: "store_*"
    table-pattern: "sale_*"
    events: ["truncate table", "drop table", "delete"]
    action: Ignore
  store-filter-rule:
    schema-pattern: "store_*"
    events: ["drop database"]
    action: Ignore

black-white-list:
  log-bak-ignored:
    ignore-tales:
    - db-name: "user"
      tbl-name: "log_bak"

mydumpers:
  global:
    threads: 4
    chunk-filesize: 64
    skip-tz-utc: true

loaders:
  global:
    pool-size: 16
    dir: "./dumped_data"

syncers:
  global:
    worker-count: 16
    batch: 100
    max-retry: 100