Asynchronous replication is real-time replication. The significant difference between Asynchronous and Synchronous replication is, Synchronous replication would wait for confirmation from the standby server that it has received all the WAL changes, and then only commit confirmation is given for the corresponding transaction, whereas in async replication master database does not wait for confirmation from standby hence if standby is not available the changes made on the master will not be replicated to standby database and may create the possibility of data loss.