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This paper presents DLHT, a concurrent in-memory hashtable. Despite efforts to optimize hashtables, that go as far as sacrificing core functionality, state-of-the-art designs still incur multiple memory accesses per request and block request processing in three cases. First, most hashtables block while waiting for data to be retrieved from memory. Second, open-addressing designs, which represent the current state-of-the-art, either cannot free index slots on deletes or must block all requests to do so. Third, index resizes block every request until all objects are copied to the new index. Defying folklore wisdom, DLHT forgoes open-addressing and adopts a fully-featured and memory-aware closed-addressing design based on bounded cache-line-chaining. This design offers (1) lock-free index operations and deletes that free slots instantly, (2) completes most requests with a single memory access, (3) utilizes software prefetching to hide memory latencies, and (4) employs a novel non-blocking and parallel resizing. In a commodity server and a memory-resident workload, DLHT surpasses 1.6B requests per second and provides 3.5×(12×) the throughput of the state-of-the-art closed-addressing (open-addressing) resizable hashtable on Gets (Deletes).
Bio:
Antonis is a Principal Researcher at Huawei, working on next-generation databases. His interests include concurrency, consistency, fault tolerance, data structures as well as transactional and analytical databases. He is particularly fond of maximizing performance per cost by exploring hardware-software co-design, combining theory with practice, and cross-pollinating ideas across databases, systems, architecture, and networking. Before Huawei, he worked for Microsoft Research and got his Ph.D. from the University of Edinburgh, for which he received the ACM-Eurosys Roger Needham HM award. His research has also received other awards, including a PPoPP Best Paper nominee and the IEEE Micro Top Picks HM.
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