So far, asynchronous replication has been covered in reasonable detail. However, asynchronous replication means that a commit on the slave is allowed to happen after the commit on the master. If a master crashes, data that has not made it to the slave yet might be lost even if replication is occurring.
Synchronous replication is here to solve the problem – if PostgreSQL replicates synchronously, a commit has to be flushed to disk by at least one replica to go through on the master. Therefore, synchronous replication basically reduces the odds of data loss substantially.
In PostgreSQL, configuring synchronous replication is easy. Only two things have to be done (in any order):
- Adjust the synchronous_standby_names setting in the postgresql.conf file on the master.
- Add an application_name setting to the primary_conninfo parameter in the config file in the replica.
Let's get started with the postgresql.conf file on the master:
synchronous_standby_names...