modes of locking:exclusive,sharetypes of locks:dml,ddl,internalv$lock type tm:id1 -> table and meterailize logv$lock type tx:id1 -> high 16 bit =xidusn(v$transaction) low 16 bit = xidslot(v$transaction)v$lock v$transaction v$sessiontools:v$lock v$locked_object dba_waiters dba_blockers
