System and method for adjusting membership of a data replication group

A method, comprising:

• performing, by a computer:
• propagating, by a master replica of a replica group that comprises two or more replicas, metadata indicating a membership change for the replica group to the other replicas of the replica group, wherein the metadata comprises a membership version indicator, wherein the two or more replicas store data on behalf of a client of a data store service on respective computing nodes of a plurality of computing nodes that implement a data store, wherein at most one of the replicas in the replica group can act as the master replica of the replica group at a time, and wherein replicas in the replica group that are not acting as the master replica act as slave replicas in the replica group;
• determining, by the master replica, whether the propagation of the metadata indicating the membership change is durable in the replica group, wherein said determining that the propagation of the metadata indicating the membership change is durable comprises determining that a pre-determined durability requirement for the replica group is met, and wherein the pre-determined durability requirement is a durability requirement that is applicable to replicated write operations initiated in response to receiving write requests from one or more clients of the data store and is applicable to replicated write operations for indicating membership changes such that the same durability requirement is applicable to replicated write operations for client write requests as well as for replicated write operations for indicating membership changes;
• and
• committing, by the master replica, the membership change in the data store, wherein said committing is performed in response to determining that the propagation of the metadata indicating the membership change is durable in the replica group.

A non-transitory, computer-readable storage medium storing program instructions that when executed on one or more computers cause the one or more computers to perform:

• maintaining data on behalf of a client of a distributed data store in the distributed data store, wherein maintaining the data comprises maintaining two or more replicas of the data stored on respective computing nodes, wherein the two or more replicas make up a replica group, wherein at most one of the replicas in the replica group can act as a master replica for the replica group at a time, wherein replicas in the replica group that are not acting as the master replica act as slave replicas in the replica group, and wherein one of the replicas acts as master replica for the replica group;
• the master replica:
• determining a membership version indicator for the replica group;
• propagating metadata indicating a membership change for the replica group to the other replicas of the replica group, wherein the metadata comprises the membership version indicator, wherein said propagating comprises sending the metadata indicating the membership change to the other replicas in the replica group as a log record to be appended to respective logs maintained by each of the other replicas in the replica group, and wherein the respective logs comprise log records, each indicating an update to the data, to the membership of the replica group, or to metadata associated with the replica group;
• determining whether the propagation of the metadata indicating the membership change meets a pre-determined durability requirement in the replica group, wherein the pre-determined durability requirement is a durability requirement that is applicable to replicated write operations initiated in response to receiving write requests from one or more clients of the data store and is applicable to replicated write operations for indicating membership changes such that the same durability requirement is applicable to replicated write operations for client write requests as well as for replicated write operations for indicating membership changes;
• and
• committing the membership change in the data storage system.

A system, comprising:

• a plurality of computing nodes, each comprising at least one processor and memory, wherein the plurality of computing nodes is configured to implement a data store;
• wherein the data store stores two or more replicas of stored data on respective computing nodes in the system, wherein the two or more replicas make up a replica group, wherein at most one of the replicas in the replica group can act as a master replica for the replica group at a time, wherein replicas in the replica group that are not acting as the master replica act as slave replicas in the replica group, and wherein one of the replicas acts as master replica for the replica group;
• wherein the master replica is configured to:
• determine a membership version indicator for the replica group;
• propagate metadata indicating a membership change for the replica group to the other replicas of the replica group, wherein the metadata comprises the membership version indicator;
• determine that the propagation of the metadata indicating the membership change meets a pre-determined durability requirement in the replica group, wherein the pre-determined durability requirement is a durability requirement that is applicable to replicated write operations initiated in response to receiving write requests from one or more clients of the data store and is applicable to replicated write operations for indicating membership changes such that the same durability requirement is applicable to replicated write operations for client write requests as well as for replicated write operations for indicating membership changes;
• and
• in response to the determination that the propagation of the metadata indicating the membership change meets a pre-determined durability requirement in the replica group, commit the membership change in the data storage system, wherein said committing comprises sending an indication to the other replicas in the replica group that the other replicas in the replica group should commit the metadata indicating the membership change.