mysqldump --single-transaction

 --single-transaction
                     Creates a consistent snapshot by dumping all tables in a
                     single transaction. Works ONLY for tables stored in
                     storage engines which support multiversioning (currently
                     only InnoDB does); the dump is NOT guaranteed to be
                     consistent for other storage engines. While a
                     --single-transaction dump is in process, to ensure a
                     valid dump file (correct table contents and binary log
                     position), no other connection should use the following
                     statements: ALTER TABLE, DROP TABLE, RENAME TABLE,
                     TRUNCATE TABLE, as consistent snapshot is not isolated
                     from them. Option automatically turns off --lock-tables.

mysqldump [ --single-transaction ]

InnoDB, InnoDB purge worker, mysqldump --single-transaction