[Freeswitch-users] sofia_reg_internal.db grow bigger and bigger along with time

i found sofia_reg_internal.db grow bigger and bigger after FreeSwitch for some time. the change comes from the sip-authentication table inside this db, it always create new record for nonce for the new challenge ('407 Proxy Authentication Required') for the call from registered users. any one can help how to avoid the db grow, i'm afaid the hard disk will be full along with time... Thanks!