Adaptive transaction scheduling for transactional memory systems

Transactional memory systems are expected to enable parallel programming at lower programming complexity, while delivering improved performance over traditional lock-based systems. Nonetheless, there are certain situations where transactional memory systems could actually perform worse. Transactional memory systems can outperform locks only when the executing workloads contain sufficient parallelism. When the workload lacks inherent parallelism, launching excessive transactions can adversely degrade performance. These situations will actually become dominant in future workloads when large-scale transactions are frequently executed. In this thesis, we propose a new paradigm called adaptive transaction scheduling to address this issue. Based on the parallelism feedback from applications, our adaptive transaction scheduler dynamically dispatches and controls the number of concurrently executing transactions. In our case study, we show that our low-cost mechanism not only guarantees that hardware transactional memory systems perform no worse than a single global lock, but also significantly improves performance for both hardware and software transactional memory systems.M.S.Committee Chair: Lee, Hsien-Hsin; Committee Member: Blough, Douglas; Committee Member: Yalamanchili, Sudhaka

Ecological and evolutionary significance of novel protist lineages

Environmental molecular surveys targeting protist diversity have unveiled novel and uncultured lineages in a variety of ecosystems, ranging from completely new high-rank lineages, to new taxa moderately related to previously described organisms. The ecological roles of some of these novel taxa have been studied, showing that in certain habitats they may be responsible for critical environmental processes. Moreover, from an evolutionary perspective they still need to be included in a more accurate and wider understanding of the eukaryotic tree of life. These seminal discoveries promoted the development and use of a wide range of more in-depth culture-independent approaches to access this diversity, from metabarcoding and metagenomics to single cell genomics and FISH. Nonetheless, culturing using classical or innovative approaches is also essential to better characterize this new diversity. Ecologists and evolutionary biologists now face the challenge of apprehending the significance of this new diversity within the eukaryotic tree of life