SQS, however, throws a wrench in the works. I was initially very surprised by the paper’s description of SQS (the 2008 version). It said that a queue might hold 200 messages, but a client requesting 100 could randomly receive only 20. This is because, to provide low latency, SQS does a best-effort poll of a subset of its distributed servers and immediately returns whatever it finds. But don’t worry, the other messages aren’t lost. They sit on servers not checked in that round. But the price of this low-latency is that FIFO ordering isn’t guaranteed. The database handles this mess by making log records idempotent, and ensures that out-of-order or duplicate processing never corrupts data.
刘先明：如果做过机器学习或AI，就知道PR曲线。当曲线较平时，只能在安心、效率、场景间权衡，本质没得选。
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沙特是这几年中东最火的商务考察地，我们不是沙特本地的地接社，一个月都能接到一两个到沙特的考察团，本地地接社有时候一个月要接待近十个。所以2023、2024年，不少周边的旅行社，纷纷转战沙特做地接业务。不过，到了2025年以后，做这行的人越来越多，价格也被打下来了。