Changefeed DDL Replication
This document describes the rules and special cases of DDL replication in TiCDC.
DDL allow list
Currently, TiCDC uses an allow list to determine whether to replicate a DDL statement. Only the DDL statements in the allow list are replicated to the downstream. The DDL statements not in the allow list are not replicated.
The allow list of DDL statements supported by TiCDC is as follows:
- create database
- drop database
- create table
- drop table
- add column
- drop column
- create index / add index
- drop index
- truncate table
- modify column
- rename table
- alter column default value
- alter table comment
- rename index
- add partition
- drop partition
- truncate partition
- create view
- drop view
- alter table character set
- alter database character set
- recover table
- add primary key
- drop primary key
- rebase auto id
- alter table index visibility
- exchange partition
- reorganize partition
- alter table ttl
- alter table remove ttl
DDL replication considerations
Asynchronous execution of ADD INDEX and CREATE INDEX DDLs
When the downstream is TiDB, TiCDC executes ADD INDEX and CREATE INDEX DDL operations asynchronously to minimize the impact on changefeed replication latency. This means that, after replicating ADD INDEX and CREATE INDEX DDLs to the downstream TiDB for execution, TiCDC returns immediately without waiting for the completion of the DDL execution. This avoids blocking subsequent DML executions.
DDL replication considerations for renaming tables
Due to the lack of some context during the replication process, TiCDC has some constraints on the replication of RENAME TABLE DDLs.
Rename a single table in a DDL statement
If a DDL statement renames a single table, TiCDC only replicates the DDL statement when the old table name matches the filter rule. The following is an example.
Assume that the configuration file of your changefeed is as follows:
[filter]
rules = ['test.t*']
TiCDC processes this type of DDL as follows:
| DDL | Whether to replicate | Reason for the handling |
|---|---|---|
RENAME TABLE test.t1 TO test.t2 | Replicate | test.t1 matches the filter rule |
RENAME TABLE test.t1 TO ignore.t1 | Replicate | test.t1 matches the filter rule |
RENAME TABLE ignore.t1 TO ignore.t2 | Ignore | ignore.t1 does not match the filter rule |
RENAME TABLE test.n1 TO test.t1 | Report an error and exit the replication | test.n1 does not match the filter rule, but test.t1 matches the filter rule. This operation is illegal. In this case, refer to the error message for handling. |
RENAME TABLE ignore.t1 TO test.t1 | Report an error and exit the replication | Same reason as above. |
Rename multiple tables in a DDL statement
If a DDL statement renames multiple tables, TiCDC only replicates the DDL statement when the old database name, old table names, and the new database name all match the filter rule.
In addition, TiCDC does not support the RENAME TABLE DDL that swaps the table names. The following is an example.
Assume that the configuration file of your changefeed is as follows:
[filter]
rules = ['test.t*']
TiCDC processes this type of DDL as follows:
| DDL | Whether to replicate | Reason for the handling |
|---|---|---|
RENAME TABLE test.t1 TO test.t2, test.t3 TO test.t4 | Replicate | All database names and table names match the filter rule. |
RENAME TABLE test.t1 TO test.ignore1, test.t3 TO test.ignore2 | Replicate | The old database name, the old table names, and the new database name match the filter rule. |
RENAME TABLE test.t1 TO ignore.t1, test.t2 TO test.t22; | Report an error | The new database name ignore does not match the filter rule. |
RENAME TABLE test.t1 TO test.t4, test.t3 TO test.t1, test.t4 TO test.t3; | Report an error | The RENAME TABLE DDL swaps the names of test.t1 and test.t3 in one DDL statement, which TiCDC cannot handle correctly. In this case, refer to the error message for handling. |
DDL statement considerations
When executing cross-database DDL statements (such as CREATE TABLE db1.t1 LIKE t2) in the upstream, it is recommended that you explicitly specify all relevant database names in DDL statements (such as CREATE TABLE db1.t1 LIKE db2.t2). Otherwise, cross-database DDL statements might not be executed correctly in the downstream due to the lack of database name information.