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title: Tutorials - Exact-Once Processing
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top-nav-title: Exact-Once Processing
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.. contents:: Messaging Tutorial - Exact-Once Processing
Exact-Once Processing
Applications typically choose between `at-least-once` and `exactly-once` processing semantics.
`At-least-once` 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. `Exactly once` processing is a stricter guarantee where applications
must see the effect of processing each record exactly once. `Exactly once` 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.
This tutorial_ shows how to do `exact-once` processing.
.. _tutorial: