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| <div class="contents topic" id="messaging-tutorial-exact-once-processing"> |
| <p class="topic-title first">Messaging Tutorial - Exact-Once Processing</p> |
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| <li><a class="reference internal" href="#exact-once-processing" id="id1">Exact-Once Processing</a></li> |
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| <div class="section" id="exact-once-processing"> |
| <h2><a class="toc-backref" href="#id1">Exact-Once Processing</a></h2> |
| <p>Applications typically choose between <cite>at-least-once</cite> and <cite>exactly-once</cite> processing semantics. |
| <cite>At-least-once</cite> processing guarantees that the application will process all the log records, |
| however when the application resumes after failure, previously processed records may be re-processed |
| if they have not been acknowledged. <cite>Exactly once</cite> processing is a stricter guarantee where applications |
| must see the effect of processing each record exactly once. <cite>Exactly once</cite> semantics can be achieved |
| by maintaining reader positions together with the application state and atomically updating both the |
| reader position and the effects of the corresponding log records.</p> |
| <p>This <a class="reference external" href="https://github.com/apache/distributedlog/blob/master/distributedlog-tutorials/distributedlog-messaging/src/main/java/org/apache/distributedlog/messaging/StreamTransformer.java">tutorial</a> shows how to do <cite>exact-once</cite> processing.</p> |
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