Prompt:
What is a State in Apache Beam?
Response:
[State](https://beam.apache.org/documentation/basics/#state-and-timers) in Apache Beam is an API that allows for managing per-key state in element-wise operations like [ParDo](https://beam.apache.org/documentation/programming-guide/#pardo) or Map. It enables fine-grained control over aggregations, particularly in situations where [windowing](https://beam.apache.org/documentation/programming-guide/#windowing) and [triggers](https://beam.apache.org/documentation/programming-guide/#triggers) are insufficient.

State is [scoped](https://beam.apache.org/documentation/programming-guide/#state-and-timers) to the current processing key within a window, meaning each key has its own state. State is particularly useful for complex aggregations across multiple elements.

Beam provides several [types of state](https://beam.apache.org/documentation/programming-guide/#types-of-state) that can be used for different use cases, including scalar and collection values:
- ValueState
- BagState
- SetState
- MapState
- OrderedListState
- CombiningState

The per-key state needs to be garbage collected, because the increasing size of the state can negatively impact performance. For more information about common garbage collection strategies, see [Garbage collecting state](https://beam.apache.org/documentation/programming-guide/#garbage-collecting-state) .

For more information, read the community blog post about [Stateful Processing](https://beam.apache.org/blog/stateful-processing/).

For additional examples of using State in Apache Beam see [State and Time examples](https://beam.apache.org/documentation/programming-guide/#state-timers-examples).