
Building Big Data Pipelines with Apache Beam
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This section will focus on a theoretical description of the stateful ParDo
transform, which is the most complex transform that a typical user of Beam needs to understand. We will divide this section into two subsections. First, we will describe its theoretical properties and the differences from the stateless version of ParDo
. Then, we will see how this theoretical knowledge applies to API changes.
As we have seen, the main difference between a stateful ParDo
object and a stateless ParDo
object is – as the name suggests – the presence of user state or timers. This alone brings one important requirement: every meaningful access to a state must be keyed. That is to say, the PCollection
object we apply to a stateful ParDo
object must be of the KV<K, V>
type. We must assign a key to every element of a PCollection
object (or use...