Sets the cluster name that appears in the process title for all server processes in this cluster. The name can be any string of less than
NAMEDATALEN characters (64 characters in a standard build). Only printable ASCII characters may be used in the
cluster_name value. Other characters will be replaced with question marks (
?). No name is shown if this parameter is set to the empty string
'' (which is the default). This parameter can only be set at server start.