Wrong output for two deprecated system variables

[gengliqi]

Bug Report

tidb_enable_tiflash_read_for_write_stmt and tidb_enable_exchange_partition are two deprecated system variables. They should be always ON.
However, the output of select @@xxx seems the set operation takes effect(but it's not).

1. Minimal reproduce step (Required)

mysql> select @@tidb_enable_tiflash_read_for_write_stmt;
mysql> set tidb_enable_tiflash_read_for_write_stmt=off;
mysql> select @@tidb_enable_tiflash_read_for_write_stmt;

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

mysql> select @@tidb_enable_tiflash_read_for_write_stmt;
+-------------------------------------------+
| @@tidb_enable_tiflash_read_for_write_stmt |
+-------------------------------------------+
|                                         1 |
+-------------------------------------------+
1 row in set (0.00 sec)

mysql> set tidb_enable_tiflash_read_for_write_stmt=off;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> select @@tidb_enable_tiflash_read_for_write_stmt;
+-------------------------------------------+
| @@tidb_enable_tiflash_read_for_write_stmt |
+-------------------------------------------+
|                                         1 |
+-------------------------------------------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

mysql> select @@tidb_enable_tiflash_read_for_write_stmt;
+-------------------------------------------+
| @@tidb_enable_tiflash_read_for_write_stmt |
+-------------------------------------------+
|                                         1 |
+-------------------------------------------+
1 row in set (0.00 sec)

mysql> set tidb_enable_tiflash_read_for_write_stmt=off;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> select @@tidb_enable_tiflash_read_for_write_stmt;
+-------------------------------------------+
| @@tidb_enable_tiflash_read_for_write_stmt |
+-------------------------------------------+
|                                         0 |
+-------------------------------------------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

master

[gengliqi]

/severity moderate

[ti-chi-bot]

@gengliqi: The label(s) affect-7.1 cannot be applied. These labels are supported: fuzz/sqlancer, challenge-program, compatibility-breaker, first-time-contributor, contribution, require-LGT3, good first issue, correctness, duplicate, proposal, security, needs-more-info, needs-cherry-pick-release-5.1, needs-cherry-pick-release-5.2, needs-cherry-pick-release-5.3, needs-cherry-pick-release-5.4, needs-cherry-pick-release-6.0, needs-cherry-pick-release-6.1, needs-cherry-pick-release-6.2, needs-cherry-pick-release-6.3, needs-cherry-pick-release-6.4, needs-cherry-pick-release-6.5, needs-cherry-pick-release-6.6, needs-cherry-pick-release-7.0, needs-cherry-pick-release-7.1, affects-5.1, affects-5.2, affects-5.3, affects-5.4, affects-6.0, affects-6.1, affects-6.2, affects-6.3, affects-6.4, affects-6.5, affects-6.6, affects-7.0, affects-7.1, may-affects-5.1, may-affects-5.2, may-affects-5.3, may-affects-5.4, may-affects-6.0, may-affects-6.1, may-affects-6.2, may-affects-6.3, may-affects-6.4, may-affects-6.5, may-affects-6.6, may-affects-7.0, may-affects-7.1.

In response to this:

/label affect-7.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[gengliqi]

/affects-7.1

[ti-chi-bot]

@gengliqi: The label(s) affect-7.1 cannot be applied. These labels are supported: fuzz/sqlancer, challenge-program, compatibility-breaker, first-time-contributor, contribution, require-LGT3, good first issue, correctness, duplicate, proposal, security, needs-more-info, needs-cherry-pick-release-5.1, needs-cherry-pick-release-5.2, needs-cherry-pick-release-5.3, needs-cherry-pick-release-5.4, needs-cherry-pick-release-6.0, needs-cherry-pick-release-6.1, needs-cherry-pick-release-6.2, needs-cherry-pick-release-6.3, needs-cherry-pick-release-6.4, needs-cherry-pick-release-6.5, needs-cherry-pick-release-6.6, needs-cherry-pick-release-7.0, needs-cherry-pick-release-7.1, affects-5.1, affects-5.2, affects-5.3, affects-5.4, affects-6.0, affects-6.1, affects-6.2, affects-6.3, affects-6.4, affects-6.5, affects-6.6, affects-7.0, affects-7.1, may-affects-5.1, may-affects-5.2, may-affects-5.3, may-affects-5.4, may-affects-6.0, may-affects-6.1, may-affects-6.2, may-affects-6.3, may-affects-6.4, may-affects-6.5, may-affects-6.6, may-affects-7.0, may-affects-7.1.

In response to this:

/label affect-7.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[gengliqi]

/label affects-7.0

[gengliqi]

/remove-label affects-7.0