I am reading tutorials on how to setup streaming replication in Postgres from master to slave.
Some tutorials recommend setting up archiving in the master (and restoring in slave) . In the master, this needs to be set in the conf file:
wal_level = hot_standby archive_mode = on archive_command = 'some rsync command to rsync logfile segments from master to slave'
What is the purpose of this archiving? When is it not necessary when setting up streaming replication?