[AlisdairO]

As they note table lock acquisition can be super painful. It's possible to write a script to use pg_stat_activity to detect that the table alteration is waiting on a lock and kill conflicting work. For some workloads the kill is unacceptable, but on highly active systems killing off a few operations is usually much less damaging than letting sessions pile up on a lock wait.

Personally I would love it if it were possible to set a mode on postgres whereby access exclusive locks break other locks and cause the transactions holding them to roll back (similar to what happens with vacuums).