SYNC mode

SYNC mode provides the most secure data protection. Two on-disk copies of data are required for transaction commit. The downside of this mode is the extra time for writing on standby and sending the ack message back to primary. In SYNC mode, logs are sent to standby only after they are written to primary disk. Log write and replication events happen sequentially. The total time for a log write is the sum of the primary_log_write, log_send, standby_log_write, and ack_message. The cost of replication is significantly higher than other modes.

Parent topic: Description of the HADR Modes