BR full restore won't rebase auto_random counter

[3pointer]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.
   BR didn't rebase auto_random after restore

   1. set tidb config auto_random to true.
   2. create table t(a int key auto_random); insert into t values (), (), ();
   3. br backup table --db t --table t --pd xxx -s xxx
   4. drop table t
   5. br restore table --db t --table t --pd xxx -s xxx
   6. insert into t values (),(),();

before backup:

MySQL [t]> select a & b'0000011111111111111111111111111' from t.t;
+----------------------------------------+
| a & b'0000011111111111111111111111111' |
+----------------------------------------+
|                                      1 |
|                                      2 |
|                                      3 |
+----------------------------------------+

2. What did you expect to see?

after restore:

select a & b'0000011111111111111111111111111' from t.t;
+----------------------------------------+
| a & b'0000011111111111111111111111111' |
+----------------------------------------+
|                                      4 |
|                                      5 |
|                                      6 |
|                                      1 |
|                                      2 |
|                                      3 |
+----------------------------------------+

3. What did you see instead?

after restore:

select a & b'0000011111111111111111111111111' from t.t;
+----------------------------------------+
| a & b'0000011111111111111111111111111' |
+----------------------------------------+
|                                      1 |
|                                      2 |
|                                      3 |
|                                      1 |
|                                      2 |
|                                      3 |
+----------------------------------------+

4. What version of BR and TiDB/TiKV/PD are you using?
   master

[bb7133]

The cause of this issue is that BR did not backup the "incremental part" of auto_random, and when restoring the data, TiDB cannot rebase the counter automatically since the restore is not in SQL layer.

In order to solve it, we need:

• For BR, backup the counter and try to restore it by an explicit rebase operation provided by TiDB(see below).
• For TiDB, provide a new DDL statement called ALTER TABLE ... AUTO_RANDOM, so the explicit rebase can be supported. The related PR has been proposed in parser: add auto_random table option support parser#823 and *: support auto_random table option tidb#16750.

It will be fixed in release v3.1.1