https://theweidi.net/tags/delivery/Recent content in Delivery on 水源一二三Hugozh-TWWed, 05 Jan 2022 06:17:34 +0000https://theweidi.net/you-cannot-have-exactly-once-delivery/Wed, 05 Jan 2022 06:11:40 +0000https://theweidi.net/you-cannot-have-exactly-once-delivery/<p><a href="https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/">https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/</a></p> <h2 id="小小摘要">小小摘要</h2> <ul> <li> <p>Distributed systems 就是 trade-offs 的權衡。</p> </li> <li> <p>（傳統）理論上不可能實作出 exactly-once delivery，任何跟你說做得出來的都是<em>唬爛</em>你或是不了解什麼是 distributed systems。實務上可以透過 idempotent （同樣的訊息處理兩次不影響）或是 deduplication 來實現同樣效果。</p> </li> <li> <p>於是我們只能從 at-most-once 跟 at-least-once 中做選擇，而大家可能都選了 at-least-once。</p> </li> </ul> <h2 id="延伸閱讀">延伸閱讀</h2> <ul> <li> <p><a href="https://queue.acm.org/detail.cfm?id=2745385">There is no now</a>in a distributed system.</p> </li> <li> <p><a href="https://www.ibm.com/cloud/learn/cap-theorem">CAP Theorem</a> = consistency, availability, and partition tolerance.</p> </li> <li> <p>Amazon SQS FIFO queue 有支援 <a href="https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/FIFO-queues-exactly-once-processing.html">exactly-once processing</a>，但實際上也是透過 deduplication 跟 acknowledgement 機制來<em>實現</em> (fake it)，如<a href="https://ably.com/blog/sqs-fifo-queues-message-ordering-and-exactly-once-processing-guaranteed">這篇</a>文章所說明。</p> </li> </ul>