learning/prompts/documentation-lookup/11_basic_state.md - beam - Git at Google


            
            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.


            Apache 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 Timers examples](https://beam.apache.org/documentation/programming-guide/#state-timers-examples).
	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.

	Apache 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 Timers examples](https://beam.apache.org/documentation/programming-guide/#state-timers-examples).