Hi there.

Our team faced issue com.github.jasync.sql.db.mysql.exceptions.MySQLException: Error 1568 - #25001 - Transaction characteristics can't be changed while a transaction is in progress
when using transaction isolation level READ_COMMITED, defined by transaction definition (not MySQL property)

Our research shows that driver sends the following commands to the database

START TRANSACTION;
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

According to MySQL documentation, this order is possible only with GLOBAL or SESSION keyword.
The correct order of commands looks like

SET autocommit = 0;
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
START TRANSACTION;

This issue affects all Spring Boot 3 projects with R2DBC version > 0.9.0 and JAsync MySQL driver.
Fix in #379