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Indirect memory accesses have irregular access patterns that limit the performance of conventional software and hardware-based prefetchers. To address this problem, we propose the Array Tracking Prefetcher (ATP), which tracks array-based indirect memory accesses using a novel combination of software and hardware. ATP is first configured by special metadata instructions, which are inserted by programmer or compiler to pass data structure traversal knowledge. It then calculates and issues prefetches based on this information. ATP also employs a novel mechanism for dynamically adjusting prefetching distance to reduce early or late prefetches. ATP yields average speedup of 2.17 as compared to a single-core without prefetching. By contrast, the speedup for conventional software and hardware-based prefetching is 1.84 and 1.32, respectively. For four cores, the average speedup for ATP is 1.85, while the corresponding speedups for software and hardwarebased prefetching are 1.60 and 1.25, respectively.

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Lookup operations for in-memory databases are heavily memory bound, because they often rely on pointer-chasing linked data structure traversals. They also have many branches that are hard-to-predict due to random key lookups. In this study, we show that although cache misses are the primary bottleneck for these applications, without a method for eliminating the branch mispredictions only a small fraction of the performance benefit is achieved through prefetching alone. We propose the Node Tracker (NT), a novel programmable prefetcher/pre-execution unit that is highly effective in exploiting inter key-lookup parallelism to improve single-thread performance. We extend NT with branch outcome streaming (BOS) to reduce branch mispredictions and show that this achieves an extra 3× speedup. Finally, we evaluate the NT as a pre-execution unit and demonstrate that we can further improve the performance in both single- and multi-threaded execution modes. Our results show that, on average, NT improves single-thread performance by 4.1× when used as a prefetcher; 11.9× as a prefetcher with BOS; 14.9× as a pre-execution unit and 18.8× as a pre-execution unit with BOS. Finally, with 24 cores of the latter version, we achieve a speedup of 203× and 11× over the single-core and 24-core baselines, respectively.