Bug #119405 Set @@transaction_isolation does not take effect.
Submitted: 17 Nov 3:12
Reporter: Sakurajima Mai Email Updates:
Status: Open Impact on me:
None 
Category:MySQL Server Severity:S3 (Non-critical)
Version:8.0.41 OS:Any
Assigned to: CPU Architecture:Any

[17 Nov 3:12] Sakurajima Mai 
Description:
mysql> SELECT @@transaction_isolation;
+-------------------------+
| @@transaction_isolation |
+-------------------------+
| READ-COMMITTED          |
+-------------------------+
1 row in set (0.00 sec)

mysql> set @@transaction_isolation = "SERIALIZABLE";
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @@transaction_isolation;
+-------------------------+
| @@transaction_isolation |
+-------------------------+
| READ-COMMITTED          |
+-------------------------+
1 row in set (0.00 sec)

How to repeat:
SELECT @@transaction_isolation;

set @@transaction_isolation = "SERIALIZABLE";

SELECT @@transaction_isolation;

Suggested fix:
mysql> set @@transaction_isolation = "SERIALIZABLE";
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @@transaction_isolation;
+-------------------------+
| @@transaction_isolation |
+-------------------------+
| SERIALIZABLE            |
+-------------------------+
1 row in set (0.00 sec)