Performing transactions in distributed transactional memory systems

A method for performing a transaction at a node in a cluster of nodes comprising one or more write operations which write to respective objects in a distributed transactional memory system, wherein the node comprises a local clock which is synchronized with a master clock of the cluster of nodes and maintains a measure of uncertainty indicating a current minimum value and a current maximum value of the master clock, the method comprising:

• reading the respective objects to be written;
• locking the respective objects to be written to by the one or more write operations;
• determining, for each of the respective objects for which locks are obtained, that the timestamp associated with that object representing a point in time has not changed since it was read;
• generating a write timestamp representing a point in time at which the write operations of the transaction are considered to occur based on the measure of uncertainty, the point in time represented by the write timestamp being after a maximum value of the master clock at the point in time that all of the respective objects to be written have been locked;
• waiting until the current minimum value of the master clock indicated by the measure of uncertainty is after the time represented by the write timestamp;
• performing the one or more write operations on the respective objects to be written to and committing the transaction by unlocking the respective objects, wherein performing the one or more write operations comprises associating the respective object to be written to with the write timestamp.

A system for use as a node in a cluster of nodes forming a distributed transactional memory system, the system comprising:

• a local clock;
• a clock synchronization module configured to synchronize the local clock with a master clock of the cluster of nodes and maintain a measure of uncertainty indicating a current minimum value and a current maximum value of the master clock;
• and
• a transaction processing module arranged to perform transactions comprising one or more read operations which read respective objects in the distributed transactional memory system by:
• generating a read timestamp from the local clock representing a point in time which is earlier than the current minimum value of the master clock, the read timestamp representing a point in time at which the read operations of the transaction are considered to occur;
• performing the one or more read operations to read the respective objects;
• determining, for each of the respective objects, whether a timestamp associated with that object representing a point in time at which that object was written indicates a time that is after the time represented by the read timestamp;
• and
• in response to determining that the timestamp associated with one of the respective objects indicates a time that is after the time represented by the read time stamp, performing an error handling procedure for that object.