※This sample exam is different from those that appear in the actual OSS-DB Exam.
PostgreSQL has supported functionality called streaming replication since version 9.0, and is now a part of the core product. Replication is an important function in large-scale systems for a number of reasons.
PostgreSQL replication facilitates PITR, where the transaction log (WAL file) is used to restore from. For this reason, the entire database cluster needs to be replicated. It is not possible to replicate individual databases in a cluster.
In replication, only one master instance can be updated. There are no restrictions on the number of read-only slave instances.
When the master instance goes down, you can promote one of the slaves to a master instance and continue to work. Therefore not only is replication for facilitating load balancing scenarios, it is also useful in high availability architectures.
When the slave instance goes down, log transfer can not be performed, but the master instance continues to operate. When the slave server is restored, all data updates will be transferred to the slave.
Therefore, the correct answers are B and D.