设定spring isolationlevel 设定了jdbc isolationlevel ,对应设定了 mysql session级别 的isolationlevel,并后面设回来
mysql> SET GLOBAL sort_buffer_size=value;
mysql> SET @@global.sort_buffer_size=value;
mysql> SET SESSION sort_buffer_size=value;
mysql> SET @@session.sort_buffer_size=value;
mysql> SET sort_buffer_size=value;(session)