`tikv_gc_safe_point` in mysql.tidb does not go forward when autocommit = 0 for global

[jackysp]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. set global autocommit = 0
2. keep on select variable_value from mysql.tidb where variable_name = 'tikv_gc_safe_point'; to check the value will change or not.

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

Value changed.

3. What did you see instead (Required)

Not changed. If I set global autocommit = 1, it will go forward again.

4. What is your TiDB version? (Required)

v5.0.1, v4.0.12

[ti-srebot]

Please edit this comment or add a new comment to complete the following information

Bug

Note: Make Sure that 'component', and 'severity' labels are added
Example for how to fill out the template: #20100

1. Root Cause Analysis (RCA) (optional)

he sessions of GC will be affected by global variables, if the user set global autocommit = 0, then saveValueToSysTable will not commit the transaction automatically, which will make the safe point could not go forward.

2. Symptom (optional)

The value of safe point in the table of mysql.tidb will not go forward, but GC will continue.

3. All Trigger Conditions (optional)

set global autocommit = 0

4. Workaround (optional)

set global autocommit = 1

5. Affected versions

[v3.0.10:v5.0.1]

6. Fixed versions

v5.0.2

[ti-srebot]

( FixedVersions AffectedVersions ) fields are empty.
The values in ( AffectedVersions ) fields are incorrect.

[ti-srebot]

( AffectedVersions ) fields are empty.
The values in ( FixedVersions AffectedVersions ) fields are incorrect.

[ti-srebot]

( AffectedVersions ) fields are empty.
The values in ( FixedVersions AffectedVersions ) fields are incorrect.