Dynamic membership management in a distributed system

A method for dynamically managing persistent membership of a coordination group in a distributed environment, the coordination group including a number of sites included in a persistent membership, with one or more of the sites including a database and a registrar, the method comprising:

• receiving, by a registrar of a first site that is a member of the persistent membership, a Membership Request from an entrant seeking to become a member of the persistent membership;
• sending, by the registrar of the first site, a Membership Change message to other sites in the coordination group so that the Membership Change message can be persisted and totally ordered;
• receiving, by the registrar of the first site, the Membership Change message in total persisted order from the coordination group;
• acquiring, by a fault tolerant distributed lock manager associated with the registrar of the first site, a distributed lock on the coordination group and entrant name;
• responsive to the register receiving the membership request, examining, by the registrar of the first site, the persistent membership to determine if a name of the entrant is already in use;
• responsive to a determination that the name of the entrant is not in use:
• disconnecting the registrar of the first site from the coordination group so that the registrar of the first site, while initializing a database for the entrant, does not apply updates to or from a database in other sites of the coordination group while the other sites are able to update at least one database in the coordination group;
• initializing the database for the entrant;
• and
• reconnecting, by the registrar of the first site, to the coordination group after initialization of the entrant database;
• responsive to a determination that the name of the entrant is in use:
• refusing, by the registrar of the first site, to proceed with initializing the database;
• aborting, by the fault tolerant distributed lock manager, any transactions in process;
• releasing, by the fault tolerant distributed lock manager, any locks held by the registrar of the first site;
• and
• disconnecting, by the registrar of the first site, from a group communication system providing an extended virtual synchrony service to the coordination group thereby allowing the registrar of the first site to provide a consistent snapshot to the entrant.

A machine-readable medium encoded with instructions, that when executed by one or more processors, cause the processor to carry out a process for dynamically managing persistent membership of a coordination group in a distributed environment, the coordination group including a number of sites included in a persistent membership, with one or more of the sites including a database and a registrar, the process comprising:

• receiving, by a registrar of a first site that is a member of the persistent membership, a Membership Request from an entrant seeking to become a member of the persistent membership;
• modifying, by the registrar of the first site, the persistent membership for the entrant;
• acquiring, by a fault tolerant distributed lock manager associated with the registrar of the first site, a distributed lock on the coordination group and entrant name;
• responsive to the register receiving the membership request, examining, by the registrar of the first site, the persistent membership to determine if a name of the entrant is already in use;
• responsive to a determination that the name of the entrant is not in use:
• disconnecting the registrar of the first site from the coordination group so that the registrar of the first site, while initializing a database for the entrant, does not apply updates to or from a database in other sites of the coordination group while the other sites are able to update at least one database in the coordination group;
• initializing the database for the entrant;
• and
• reconnecting, by the registrar of the first site, to the coordination group after initialization of the entrant database;
• responsive to a determination that the name of the entrant is in use:
• refusing, by the registrar of the first site, to proceed with initializing the database;
• aborting, by the fault tolerant distributed lock manager, any transactions in process;
• releasing, by the fault tolerant distributed lock manager, any locks held by the registrar of the first site;
• and
• disconnecting, by the registrar of the first site, from a group communication system providing an extended virtual synchrony service to the coordination group thereby allowing the registrar of the first site to provide a consistent snapshot to the entrant.