设计数据密集型应用（影印版）

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• UDP is a good choice in situations where delayed data is worthless. For example, in a VoIP phone call, there probably isn’t enough time to retransmit a lost packet before its data is due to be played over the loudspeakers. In this case, there’s no point in retransmitting the packet—the application must instead fill the missing packet’s time slot with silence (causing a brief interruption in the second) and move on in the stream. The retry happens at the human layer instead. (“Could you repeat that please? The sound just cut out for a moment.”) (查看原文)

  Jake 2赞 2021-04-30 00:53:53

• For data warehouse queries that need to scan over millions of rows, a big bottleneck is the bandwidth for getting data from disk into memory. However, that is not the only bottleneck. Developers of analytical databases also worry about efficiently using the bandwidth from main memory into the CPU cache, avoiding branch mispredictions and bubbles in the CPU instruction processing pipeline, and making use of single-instruction-multi-data (SIMD) instructions in modern CPUs. Besides reducing the volume of data that needs to be loaded from disk, columnoriented storage layouts are also good for making efficient use of CPU cycles. For example, the query engine can take a chunk of compressed column data that fits comfortably in the CPU’s L1 cache and iterate through it in a tight loop (that is, w... (查看原文)

  无心 1赞 2019-11-09 08:17:33

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