SmartMySQL Long-running transaction debugger: Among the many things that can cause a “server stall” is a long-running transaction. If a transaction remains open for a very long time without committing, and has modified data, then other transactions could block and fail with a lock wait timeout. The problem is, it can be very difficult to find the offending code so that it can be fixed. I see this much too often, and have developed a budebber module called InnoTOP with rich graphical user interface and simplified for tracking down what that long-running transaction is doing. you can easily identify related undo transaction thread ID then you can kill it for fixing issue with out any expert level DB engineer knowledge
