Group Status

Group status advisories report the state of group members.

Group members and observers can subscribe to receive group status advisories.

The group library presents members and observers with group status advisories, which can have one of three forms:
Total Status
A group status advisory that contains the group status of all existing member processes.
Change in Status
A group status advisory that contains the group status of a subset of members, including new members that joined the group, members that left the group, or members that became disconnected. Frequently, only one member at a time changes status, so the subset contains only that one member.
Server Unavailable
A group status advisory that indicates that the group service is unavailable or unreachable. This form does not contain the group status of any members.
When the state of the group changes, the group library presents members and observers with group status advisories. The form of the advisory depends on both the member and state change:
  • When a new member joins a group, it receives a total status advisory, containing the status of all the members, excluding observers. All the other members and observers receive a change in status advisory.

    When a disconnected member reconnects, this event results in the same set of status messages.

  • When a member leaves a group, it does not receive a status advisory. All the other members and observers receive a change in status advisory.
  • When a member becomes disconnected from the group service, it receives a server unavailable advisory. All the other members and observers also receive a change in status advisory.
  • When a new observer joins a group, the group state does not change. The new observer receives a total status advisory, containing the status of all the other members, excluding any observers. Other members and observers do not receive a status advisory.
  • When an observer leaves a group, or becomes disconnected from the group service, the group state does not change. The affected observer does not receive a status advisory, nor do any other members or observers.

For reference details about the group status advisory message, see GROUP_STATUS.

Related concepts
Related reference