alter table t auto_increment=xxx doesn't work properly

[cyliu0]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Reproduced on pd/tikv/tidb (3/3/3) cluster

> drop table if exists t;
> create table t (a int) shard_row_id_bits = 5;
> alter table t auto_increment = 72057594037927936;   
> insert into t set a=1;
> alter table t shard_row_id_bits = 10;
Error 1467: shard_row_id_bits 10 will cause next global auto ID 72057594039457405 overflow"
-- The error information should show 72057594037927936

mysql root@172.16.4.61:test> create table t1 (a int auto_increment primary key);
Query OK, 0 rows affected
Time: 0.563s
mysql root@172.16.4.61:test> insert into t1 values()
Query OK, 1 row affected
Time: 0.060s
mysql root@172.16.4.61:test> alter table t1 auto_increment = 10000
You're about to run a destructive command.
Do you want to proceed? (y/n): y
Your call!
Query OK, 0 rows affected
Time: 1.059s
mysql root@172.16.4.61:test> insert into t1 values()
Query OK, 1 row affected
Time: 0.057s
mysql root@172.16.4.61:test> select * from t1
+-------+
| a     |
+-------+
| 1     |
| 93497 |
+-------+
2 rows in set
Time: 0.063s

2. What did you expect to see? (Required)

> alter table t shard_row_id_bits = 10;
Error 1467: shard_row_id_bits 10 will cause next global auto ID 72057594039457405 overflow"

> select * from t1;
+-------+
| a     |
+-------+
| 1     |
| 10000 |
+-------+

3. What did you see instead (Required)

> alter table t shard_row_id_bits = 10;
Error 1467: shard_row_id_bits 10 will cause next global auto ID 72057594037927936 overflow"

> select * from t1;
+-------+
| a     |
+-------+
| 1     |
| 93497 |
+-------+

4. Affected version (Required)

mysql root@172.16.4.103:(none)> select tidb_version()
+-------------------------------------------------------------------+
| tidb_version()                                                    |
+-------------------------------------------------------------------+
| Release Version: v4.0.0-rc.2-41-g689a6b6                          |
| Edition: Community                                                |
| Git Commit Hash: 689a6b6439ae7835947fcaccf329a3fc303986cb         |
| Git Branch: release-4.0                                           |
| UTC Build Time: 2020-05-27 11:07:16                               |
| GoVersion: go1.13.10                                              |
| Race Enabled: false                                               |
| TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306 |
| Check Table Before Drop: false                                    |
+-------------------------------------------------------------------+

5. Root Cause Analysis

[bb7133]

> select * from t1;
+-------+
| a     |
+-------+
| 1     |
| 93497 |
+-------+

The value is expected because of the cache: https://docs.pingcap.com/tidb/stable/auto-increment#concept

Error 1467: shard_row_id_bits 10 will cause next global auto ID 72057594037927936 overflow"

Looks that the error message should be refined.