When you use Apache::DBI or similar persistent connections, be very careful about locking the database (LOCK TABLE ...) or single rows. MySQL threads keep tables locked until the thread ends (i.e., the connection is closed) or until the tables are explicitly unlocked. If your session dies while tables are locked, they will stay locked, as your connection to the database won't be closed. In Chapter 6 we discussed how to terminate the program cleanly if the session is aborted prematurely.