When dumping really big tables, mysqldump was using up large amounts of memory, so it may cause no-response problem. To overcome this, --quick and --single-transaction options can used. Following are the sections for these options in the mysqldump man page.
This option is useful for dumping large tables. It forces mysqldump to retrieve rows for a table from the server a row at a time rather than retrieving the entire row set and buffering it in memory before writing it out.
To dump big tables, you should combine this option with --quick.