P2-[4.0 bug hunting]-[AutoIncrement]-Restarting consumes too many values

[wwar]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

This is a regression:

DROP TABLE IF EXISTS t0;
CREATE TABLE t0 (
 id int not null primary key auto_increment,
 pad varbinary(255) not null
) auto_increment=1;
SHOW CREATE TABLE t0\G
INSERT INTO t0 VALUES (NULL, 'a');
SHOW CREATE TABLE t0\G
-- restart tidb-server
INSERT INTO t0 VALUES (NULL, 'a');
SELECT * FROM t0;

2. What did you expect to see?

TiDB 2.1.2 (the version I had on hand):

mysql> select * from t0;
+-------+-----+
| id    | pad |
+-------+-----+
|     1 | a   |
| 30001 | a   |
+-------+-----+
2 rows in set (0.00 sec)

3. What did you see instead?

TiDB 4.0:

mysql> SELECT * FROM t0;
+---------+-----+
| id      | pad |
+---------+-----+
|       1 | a   |
| 2000001 | a   |
+---------+-----+
2 rows in set (0.00 sec)

Because integers default to signed, that is 1/1000th of the keyspace consumed. It looks like the next restart only consumes 30000 values, which is better. But I haven't tested with multiple tidb-servers:

mysql> show create table t0\G
*************************** 1. row ***************************
       Table: t0
Create Table: CREATE TABLE `t0` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `pad` varbinary(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin AUTO_INCREMENT=2030001
1 row in set (0.00 sec)

4. What version of TiDB are you using? (tidb-server -V or run select tidb_version(); on TiDB)

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-352-g5ede18f10
Git Commit Hash: 5ede18f10eedfe2e3690d7728dec3ffa4b0af2d5
Git Branch: master
UTC Build Time: 2020-04-24 03:45:17
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.01 sec)

[shuke987]

are there any other TiDB instances doing some insertions?

[wwar]

No, this is just a minimal install: 1x tidb 1x tikv 1x pd.

I have switched from tiup temporarily to my previous script of downloading wget http://download.pingcap.org/tidb-nightly-linux-amd64.tar.gz. It seems that tiup nightly is currently a few days behind.

[shuke987]

This is in line with current product design, but the design may be defective

[shuke987]

/bug P2