FLASHBACK CLUSTER TO TIMESTAMP

TiDB v6.4.0 introduces the FLASHBACK CLUSTER TO TIMESTAMP syntax. You can use it to restore a cluster to a specific point in time.

Syntax

FLASHBACK CLUSTER TO TIMESTAMP '2022-09-21 16:02:50';

Synopsis

FlashbackToTimestampStmt ::=
    "FLASHBACK" "CLUSTER" "TO" "TIMESTAMP" stringLit

Notes

• The time specified in the FLASHBACK statement must be within the Garbage Collection (GC) lifetime. The system variable tidb_gc_life_time (default: 10m0s) defines the retention time of earlier versions of rows. The current safePoint of where garbage collection has been performed up to can be obtained with the following query:

  SELECT * FROM mysql.tidb WHERE variable_name = 'tikv_gc_safe_point';
  

• Only a user with the SUPER privilege can execute the FLASHBACK CLUSTER SQL statement.
• FLASHBACK CLUSTER does not support rolling back DDL statements that modify PD-related information, such as ALTER TABLE ATTRIBUTE, ALTER TABLE REPLICA, and CREATE PLACEMENT POLICY.
• At the time specified in the FLASHBACK statement, there cannot be a DDL statement that is not completely executed. If such a DDL exists, TiDB will reject it.
• Before executing FLASHBACK CLUSTER TO TIMESTAMP, TiDB disconnects all related connections and prohibits read and write operations on these tables until the FLASHBACK CLUSTER statement is completed.
• The FLASHBACK CLUSTER TO TIMESTAMP statement cannot be canceled after being executed. TiDB will keep retrying until it succeeds.
• During the execution of FLASHBACK CLUSTER, if you need to back up data, you can only use Backup & Restore and specify a BackupTS that is earlier than the start time of FLASHBACK CLUSTER. In addition, during the execution of FLASHBACK CLUSTER, enabling log backup will fail. Therefore, try to enable log backup after FLASHBACK CLUSTER is completed.
• If the FLASHBACK CLUSTER statement causes the rollback of metadata (table structure, database structure), the related modifications will not be replicated by TiCDC. Therefore, you need to pause the task manually, wait for the completion of FLASHBACK CLUSTER, and manually replicate the schema definitions of the upstream and downstream to make sure that they are consistent. After that, you need to recreate the TiCDC changefeed.

• Only a user with the SUPER privilege can execute the FLASHBACK CLUSTER SQL statement.
• FLASHBACK CLUSTER does not support rolling back DDL statements that modify PD-related information, such as ALTER TABLE ATTRIBUTE, ALTER TABLE REPLICA, and CREATE PLACEMENT POLICY.
• At the time specified in the FLASHBACK statement, there cannot be a DDL statement that is not completely executed. If such a DDL exists, TiDB will reject it.
• Before executing FLASHBACK CLUSTER TO TIMESTAMP, TiDB disconnects all related connections and prohibits read and write operations on these tables until the FLASHBACK CLUSTER statement is completed.
• The FLASHBACK CLUSTER TO TIMESTAMP statement cannot be canceled after being executed. TiDB will keep retrying until it succeeds.
• If the FLASHBACK CLUSTER statement causes the rollback of metadata (table structure, database structure), the related modifications will not be replicated by TiCDC. Therefore, you need to pause the task manually, wait for the completion of FLASHBACK CLUSTER, and manually replicate the schema definitions of the upstream and downstream to make sure that they are consistent. After that, you need to recreate the TiCDC changefeed.

Example

The following example shows how to restore the newly inserted data:

mysql> CREATE TABLE t(a INT);
Query OK, 0 rows affected (0.09 sec)

mysql> SELECT * FROM t;
Empty set (0.01 sec)

mysql> SELECT now();
+---------------------+
| now()               |
+---------------------+
| 2022-09-28 17:24:16 |
+---------------------+
1 row in set (0.02 sec)

mysql> INSERT INTO t VALUES (1);
Query OK, 1 row affected (0.02 sec)

mysql> SELECT * FROM t;
+------+
| a    |
+------+
|    1 |
+------+
1 row in set (0.01 sec)

mysql> FLASHBACK CLUSTER TO TIMESTAMP '2022-09-28 17:24:16';
Query OK, 0 rows affected (0.20 sec)

mysql> SELECT * FROM t;
Empty set (0.00 sec)

If there is a DDL statement that is not completely executed at the time specified in the FLASHBACK statement, the FLASHBACK statement fails:

mysql> ALTER TABLE t ADD INDEX k(a);
Query OK, 0 rows affected (0.56 sec)

mysql> ADMIN SHOW DDL JOBS 1;
+--------+---------+-----------------------+------------------------+--------------+-----------+----------+-----------+---------------------+---------------------+---------------------+--------+
| JOB_ID | DB_NAME | TABLE_NAME            | JOB_TYPE               | SCHEMA_STATE | SCHEMA_ID | TABLE_ID | ROW_COUNT | CREATE_TIME         | START_TIME          | END_TIME            | STATE  |
+--------+---------+-----------------------+------------------------+--------------+-----------+----------+-----------+---------------------+---------------------+---------------------+--------+
|     84 | test    | t                     | add index /* ingest */ | public       |         2 |       82 |         0 | 2023-01-29 14:33:11 | 2023-01-29 14:33:11 | 2023-01-29 14:33:12 | synced |
+--------+---------+-----------------------+------------------------+--------------+-----------+----------+-----------+---------------------+---------------------+---------------------+--------+
1 rows in set (0.01 sec)

mysql> FLASHBACK CLUSTER TO TIMESTAMP '2023-01-29 14:33:12';
ERROR 1105 (HY000): Detected another DDL job at 2023-01-29 14:33:12 +0800 CST, can't do flashback

Through the log, you can obtain the execution progress of FLASHBACK. The following is an example:

[2022/10/09 17:25:59.316 +08:00] [INFO] [cluster.go:463] ["flashback cluster stats"] ["complete regions"=9] ["total regions"=10] []

MySQL compatibility

This statement is a TiDB extension to MySQL syntax.