synchronous=primary database wait to sent completed information to end user until redo to recover write both primary and at least standby database.this mode is required for maximum availability and maximum protection mode.
asynchronous=primary database sent info to end user if commit is successful whether redo data to recover write to standby database.
SYNC mode synchronizes the primary with the standby database and all DML on the primary server will NOT be committed until the logs have been successfully transported to the standby servers. The synchronous log transport mode is required for the Maximum Protection and Maximum Availability data protection modes.
ASYNC allows updates (DML) to be committed on the primary server before the log file arrives on the standby servers. The asynchronous log transport mode is required for the Maximum Performance data protection mode.
Please close your old questions to keep the forum clean. You have 14 questions this month all OPEN. With all due respect this is NOT cool.