Two table ids are allocated when creating a table, but only one is used.

[mjonss]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

tidb> create table t1 (a int);
Query OK, 0 rows affected (0.09 sec)

tidb> create table t2 (a int);
Query OK, 0 rows affected (0.08 sec)

tidb> SELECT TABLE_NAME, START_KEY, END_KEY FROM information_schema.TIKV_REGION_STATUS WHERE TABLE_NAME IN ('t1', 't2');
+------------+--------------------------------------+--------------------------------------+
| TABLE_NAME | START_KEY                            | END_KEY                              |
+------------+--------------------------------------+--------------------------------------+
| t1         | 7480000000000000FF6600000000000000F8 | 7480000000000000FF6800000000000000F8 |
| t2         | 7480000000000000FF6800000000000000F8 | 748000FFFFFFFFFFFFF900000000000000F8 |
+------------+--------------------------------------+--------------------------------------+
2 rows in set (0.00 sec)

tidb> select table_name, tidb_table_id from information_schema.tables where table_name in ('t1', 't2');
+------------+---------------+
| table_name | tidb_table_id |
+------------+---------------+
| t1         |           102 |
| t2         |           104 |
+------------+---------------+
2 rows in set (0.01 sec)

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

Consecutive table ids, not a gap of one id (wasted one table id).

3. What did you see instead (Required)

Two table ids used when creating a single table.
Also the region end key is table_id + 2, what can be between table_id +1 .. table_id +2?

4. What is your TiDB version? (Required)

tidb_version(): Release Version: v7.6.0-alpha
Edition: Community
Git Commit Hash: 3f94666b4bafd903886b89206ac603d26d9a9e87
Git Branch: heads/refs/tags/v7.6.0-alpha
UTC Build Time: 2023-11-18 14:26:36
GoVersion: go1.21.3
Race Enabled: false
Check Table Before Drop: false
Store: tikv

[Defined2014]

Because the DDL job id and table id use the same allocator. So the it will have a gap between two tables. Maybe it's by design.
They both use func (m *Meta) GenGlobalIDs(n int) ([]int64, error) to get id from TiKV.
/cc @zimulala

[zimulala]

@Defined2014
Yeah, it was designed that way from the beginning

[Defined2014]

Because the DDL job id and table id use the same allocator. So the it will have a gap between two tables. Maybe it's by design. They both use func (m *Meta) GenGlobalIDs(n int) ([]int64, error) to get id from TiKV. /cc @zimulala

@Defined2014 Yeah, it was designed that way from the beginning

According to what was mentioned above, I will change the type to enhancement first.