Just need to make sure that grails calls shutdown() on the hsql database during context destruction? If this issue is addressed, this will ensure that this Thread is cleaned up properly and a potential leak is avoided in a hot-deploy environment.
if(dbName == 'HSQL Database Engine') { connection.createStatement().executeUpdate('SHUTDOWN') }
if(dbName == 'HSQL Database Engine') { connection.createStatement().executeUpdate('SHUTDOWN') }