There are special error codes and status reports dealing with cluster failures.
The status function with an argument of 'cluster_d' shows a host by host report of the cluster:
SQL> status ('cluster_d');
If all is normal, the message is as described in the cluster administration section. If some hosts are down, meaning that they do not accept network connections at the cluster port, these are first listed as being down. Then follows the summary status line and a status line for all the hosts that can be connected to.
A host being contactable over the cluster protocol does not mean that it is online or in sync with the rest.
If a physical cluster has no logical clusters that are in duplicate, there is no redundancy, except for the built in redundancy of schema.
If a host is not in the online state, an extra line in the cluster status report describes the state in more detail. The state can be one of:
roll forward - The host is recovering from log. The count of transactions replayed to date is shown after this.
removed - The host is considered down and no attempt is made to contact it until it explicitly rejoins the cluster. This is controlled with the cl_host_enable function.
It is possible that the host considers itself in one state and the host showing the report thinks that it is in some other state. If this is so, the status report mentions it.
Applications see cluster failures through the following SQL states:
08C01 - A host cannot be contacted or can be contacted but is not in the online state
08C02 - An operation that previously had a connection to a host finds that it no longer has the connection.
08C03 - A master only operation was tried on a non-master. Indicates possibility of divergent understanding of master succession. This is expected to reset itself.
08C04 - A write was attempted on a partition that is flagged read only, as per cl_read_only.
08C05 - A request was refused because the host serving the request thinks the requesting host is not admitted to cluster as per cl_host_enable, i.e. was removed and not reintroduced.
08C06 - A cluster operation was not made because the host thinks it is not joined to the cluster either because it has not finished roll forward or because it is marked removed by ch_host_enable.