FLASHBACK CLUSTER

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. When specifying the timestamp, you can either set a datetime value or use a time function. The format of datetime is like '2016-10-08 16:45:26.999', with millisecond as the minimum time unit. But in most cases, specifying the timestamp with second as the time unit is sufficient, for example, '2016-10-08 16:45:26'.

Starting from v6.5.6, TiDB introduces the FLASHBACK CLUSTER TO TSO syntax. This syntax enables you to use TSO to specify a more precise recovery point in time, thereby enhancing flexibility in data recovery.

Syntax

FLASHBACK CLUSTER TO TIMESTAMP '2022-09-21 16:02:50';
FLASHBACK CLUSTER TO TSO 445494839813079041;

Synopsis

FlashbackToTimestampStmt
         ::= 'FLASHBACK' 'CLUSTER' 'TO' 'TIMESTAMP' stringLit
           | 'FLASHBACK' 'CLUSTER' 'TO' 'TSO' LengthNum

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.

• From the time specified in the FLASHBACK statement to the time when the FLASHBACK is executed, there cannot be a DDL statement that changes the related table structure. If such a DDL exists, TiDB will reject it.

• Before executing FLASHBACK CLUSTER, TiDB disconnects all related connections and prohibits read and write operations on these tables until the FLASHBACK statement is completed.

• The FLASHBACK CLUSTER statement cannot be canceled after being executed. TiDB will keep retrying until it succeeds.

Example

The following example shows how to flashback a cluster to a specific timestamp to restore 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)

The following example shows how to flashback a cluster to a specific TSO to precisely restore mistakenly deleted data:

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> BEGIN;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @@tidb_current_ts;  -- Get the current TSO
+--------------------+
| @@tidb_current_ts  |
+--------------------+
| 446113975683252225 |
+--------------------+
1 row in set (0.00 sec)

mysql> ROLLBACK;
Query OK, 0 rows affected (0.00 sec)


mysql> DELETE FROM t;
Query OK, 1 rows affected (0.00 sec)


mysql> FLASHBACK CLUSTER TO TSO 446113975683252225;
Query OK, 0 rows affected (0.20 sec)

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

If there is a DDL statement that changes the table structure from the time specified in the FLASHBACK statement to the time when the FLASHBACK is executed, the FLASHBACK statement fails:

mysql> SELECT now();
+---------------------+
| now()               |
+---------------------+
| 2022-10-09 16:40:51 |
+---------------------+
1 row in set (0.01 sec)

mysql> CREATE TABLE t(a int);
Query OK, 0 rows affected (0.12 sec)

mysql> FLASHBACK CLUSTER TO TIMESTAMP '2022-10-09 16:40:51';
ERROR 1105 (HY000): Detected schema change due to another DDL job during [2022-10-09 16:40:51 +0800 CST, now), can't do flashback

The FLASHBACK execution progress can be viewed via the Raft admin > Peer in Flashback State metrics and the log. The following log is an example:

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.