EPO-R: An Efficient Garbage Collection Scheme for Long-Term Transactions

This paper proposes EPO-R that is an efficient garbage collection scheme designed for multi-version concurrency control (MVCC) protocols. MVCC generates a version for each update operation and it can exhaust physical memory for dynamically changing environments such as IoT payments. EPO is a novel garbage collection technique for long-term transactions. We found room for improvement in EPO, which is the trigger of reclamation invocation. EPO is triggered for each write operation and it wastes CPU resource. The proposed method EPO-R is triggered on a read operation to address this issue. The result of experiments with 224 CPU cores and workloads with the combination of short-term and long term-transactions demonstrated that EPO-R exhibited 3.4 times higher throughput than that of EPO. The reason for this can be explained by analyzing the number of unreclaimable versions.