The<b>stream-tableduality</b> describes the close relationship between streams and tables.
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Let's illustrate this with an example. Imagine a table that tracks the total number of pageviews by user (first column of diagram below). Over time, whenever a new pageview event is processed, the state of the table is updated accordingly. Here, the state changes between different points in time - and different revisions of the table - can be represented as a changelog stream (second column).
The same mechanism is used, for example, to replicate databases via change data capture (CDC) and, within Kafka Streams, to replicate its so-called state stores across machines for fault-tolerance.
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Itisimportanttounderstandthatthestateofyourapplication--tobeextraclear,wemightcallit"the full state of the entire application"--istypicallysplitacrossmanydistributedinstancesofyourapplication,andthusacrossmanystatestoresthataremanagedlocallybytheseapplicationinstances.