Tales From A Lazy Fat DBA

Data Guard synchronous (SYNC) vs asynchronous (ASYNC) modes

Oracle Data Guard redo log transport offers synchronous log transport mode (LogXptMode = ‘SYNC’) or asynchronous log transport mode (LogXptMode = ‘ASYNC’).  Systems with a network bottleneck would get better overall response time with the ASYNC mode, while shops that cannot tolerate a stale standby server (i.e. maximum availability or maximum protection are best with the SYNC mode.

The difference is all about when the COMMIT happens.

LogXptMode = (‘SYNC‘):  As the name implies, 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.
LogXptMode = (‘ASYNC‘):  Conversely, asynchronous mode (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.

To check status of log export mode on database.

DGMGRL> show database qrcl logxptmode;
show database qrcl logxptmode;
LogXptMode = ‘ASYNC’
DGMGRL>

To edit logxptmode:

DGMGRL> edit database ‘qrcl’ set property ‘logxptmode’=’ASYNC’;
edit database ‘qrcl’ set property ‘logxptmode’=’ASYNC’;
Property “logxptmode” updated