A new type of logs, the command log, is being employed to replace the traditional data log (e.g., ARIES log) in the in-memory databases. Instead of recording how the tuples are updated, a command log only tracks the transactions being executed, there
by effectively reducing the size of the log and improving the performance. Command logging on the other hand increases the cost of recovery, because all the transactions in the log after the last checkpoint must be completely redone in case of a failure. In this paper, we first extend the command logging technique to a distributed environment, where all the nodes can perform recovery in parallel. We then propose an adaptive logging approach by combining data logging and command logging. The percentage of data logging versus command logging becomes an optimization between the performance of transaction processing and recovery to suit different OLTP applications. Our experimental study compares the performance of our proposed adaptive logging, ARIES-style data logging and command logging on top of H-Store. The results show that adaptive logging can achieve a 10x boost for recovery and a transaction throughput that is comparable to that of command logging.
Multicore CPUs and large memories are increasingly becoming the norm in modern computer systems. However, current database management systems (DBMSs) are generally ineffective in exploiting the parallelism of such systems. In particular, contention c
an lead to a dramatic fall in performance. In this paper, we propose a new concurrency control protocol called DGCC (Dependency Graph based Concurrency Control) that separates concurrency control from execution. DGCC builds dependency graphs for batched transactions before executing them. Using these graphs, contentions within the same batch of transactions are resolved before execution. As a result, the execution of the transactions does not need to deal with contention while maintaining full equivalence to that of serialized execution. This better exploits multicore hardware and achieves higher level of parallelism. To facilitate DGCC, we have also proposed a system architecture that does not have certain centralized control components yielding better scalability, as well as supports a more efficient recovery mechanism. Our extensive experimental study shows that DGCC achieves up to four times higher throughput compared to that of state-of-the-art concurrency control protocols for high contention workloads.
