SET GLOBAL tidb_skip_isolation_level_check=1 doesn't work as expected

[sunxiaoguang]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> SET GLOBAL tidb_skip_isolation_level_check=1;
Query OK, 0 rows affected (0.02 sec)

Disconnect and reconnect to TiDB

mysql> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
ERROR 8048 (HY000): The isolation level 'SERIALIZABLE' is not supported. Set tidb_skip_isolation_level_check=1 to skip this error

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

mysql> SET GLOBAL tidb_skip_isolation_level_check=1;
Query OK, 0 rows affected (0.03 sec)

Disconnect and reconnect to TiDB

mysql> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
Query OK, 0 rows affected, 1 warning (0.00 sec)

3. What did you see instead (Required)

mysql> SET GLOBAL tidb_skip_isolation_level_check=1;
Query OK, 0 rows affected (0.02 sec)

Disconnect and reconnect to TiDB

mysql> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
ERROR 8048 (HY000): The isolation level 'SERIALIZABLE' is not supported. Set tidb_skip_isolation_level_check=1 to skip this error

4. What is your TiDB version? (Required)

5.1.0 and all the new versions

[morgo]

I commented on the PR, but I'm not sure this is a bug. GLOBAL scoped changes are not supposed to apply to the current session yet. They only apply to new sessions.

[sunxiaoguang]

I commented on the PR, but I'm not sure this is a bug. GLOBAL scoped changes are not supposed to apply to the current session yet. They only apply to new sessions.

Oops, you are right. I agree that global changes should not affect current session. However I saw something strange that there might be some other issue as well.

The first time I restart client to check global variables and change isolation level to SERIALIZABLE without having trouble. However the second time it stopped working again with tidb_skip_isolation_level_check=1 configured.

I will take another look to this.

[sunxiaoguang]

I commented on the PR, but I'm not sure this is a bug. GLOBAL scoped changes are not supposed to apply to the current session yet. They only apply to new sessions.

After checking comments in PR, I realized that you already pointed out the root cause. My last experiment failed because I didn't read variable to force reload from global before changing isolation level. Simply remove skipInit from TiDBSkipIsolationLevelCheck definition works well. Thanks! @morgo

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'backport-x.y.z',
and then remove 'needs-more-info' label.

[sunxiaoguang]

/label affects-5.1

[ti-chi-bot]

@sunxiaoguang: The label(s) affects-5.1 cannot be applied. These labels are supported: CHANGELOG, challenge-program, compatibility-breaker, contribution, correctness, first-time-contributor, good-first-issue, hacktoberfest, high-performance, hptc, need-more-info, needs-cherry-pick-3.0, needs-cherry-pick-3.1, needs-cherry-pick-4.0, needs-cherry-pick-5.0, needs-cherry-pick-5.1, needs-cherry-pick-5.2, proposal, release-note, require-LGT3, security, tools.

In response to this:

/label affects-5.1

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.

[sunxiaoguang]

/label affects-5.2

[ti-chi-bot]

@sunxiaoguang: The label(s) affects-5.2 cannot be applied. These labels are supported: CHANGELOG, challenge-program, compatibility-breaker, contribution, correctness, first-time-contributor, good-first-issue, hacktoberfest, high-performance, hptc, need-more-info, needs-cherry-pick-3.0, needs-cherry-pick-3.1, needs-cherry-pick-4.0, needs-cherry-pick-5.0, needs-cherry-pick-5.1, needs-cherry-pick-5.2, proposal, release-note, require-LGT3, security, tools.

In response to this:

/label affects-5.2

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.

[sunxiaoguang]

/label needs-cherry-pick-5.1

[sunxiaoguang]

/label needs-cherry-pick-5.2