Replication Mode

Instaclustr managed PostgreSQL clusters support SYNCHRONOUS and ASYNCHRONOUS replication modes. This setting can be selected during the creation of a cluster and would default to SYNCHRONOUS if not specified. 

SYNCHRONOUS

This mode will ensure by default that confirmation of a committed transaction will only be returned to the client, once the replicas have written the transaction to their write-ahead logs. This is achieved by making sure all replicas are kept in the synchronous_standby_names of the primary and the synchronous_commit option is set to the value on. 

Clients will be able to lower the level of synchronisation by setting the synchronous_commit option within a transaction, however it is expected that clients keep the default to ensure data retention for transactions that are required to be retained during a failover. 

ASYNCHRONOUS

This mode will configure replication such that confirmation of a committed transaction will not wait for the replicas to acknowledge, which would in general make your transactions faster than a synchronous setup. For this option, synchronous_standby_names will not be populated. 

With asynchronous replication, it should be noted that transaction loss is possible on failovers, given that the promoted replica may not have the latest updates. Selection of this mode will affect service level agreements related to data loss tolerance.