On some platforms, if set to true, prevents Derby from booting a database if a db.lck file is present in the database directory.
Derby attempts to prevent two JVMs from accessing a database at one time (and potentially corrupting it) with the use of a file called db.lck in the database directory. On some operating systems, the use of a lock file does not guarantee single access, and so Derby only issues a warning and might allow multiple JVM access even when the file is present. (For more information, see "Double-Booting System Behavior" in Chapter 1 of the Java DB Developer's Guide.)
This property is static; if you change it while Derby is running, the change does not take effect until you reboot.