Restate lets you persist key-value (K/V) state using its embedded K/V store.

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Key characteristics

Learn about Restate’s embedded K/V store.
State is only available for Virtual Objects and Workflows. Scope & retention:
  • For Virtual Objects: State is scoped per object key and retained indefinitely. It is persisted and shared across all invocations for that object until explicitly cleared.
  • For Workflows: State is scoped per workflow execution (workflow ID) and retained only for the duration of the workflow’s configured retention time.
Access Rules: You can inspect and edit the K/V state via the UI and the CLI.

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List all state keys

To retrieve all keys for which the current Virtual Object has stored state: 
Collection<String> keys = ctx.stateKeys();

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Get state value

To read a value by key. 
// Getting String value
StateKey<String> STRING_STATE_KEY = StateKey.of("my-key", String.class);
String stringState = ctx.get(STRING_STATE_KEY).orElse("my-default");

// Getting integer value
StateKey<Integer> INT_STATE_KEY = StateKey.of("my-key", Integer.class);
int intState = ctx.get(INT_STATE_KEY).orElse(0);
See the serialization docs to customize the state serializer.

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Set state value

To write or update a value: 
StateKey<String> STRING_STATE_KEY = StateKey.of("my-key", String.class);
ctx.set(STRING_STATE_KEY, "my-new-value");

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Clear state key

To delete a specific key: 
StateKey<String> STRING_STATE_KEY = StateKey.of("my-key", String.class);
ctx.clear(STRING_STATE_KEY);

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Clear all state keys

To remove all stored state for the current Virtual Object: 
ctx.clearAll();

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Advanced: Eager vs. lazy state loading

Restate supports two modes for loading state in handlers:

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Eager state (default)

  • How it works: State is automatically sent with the request when invoking a handler
  • Benefits: State is available immediately when the handler starts executing
  • Behavior: All reads and writes to state are local to the handler execution
  • Best for: Small to medium state objects that are frequently accessed

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Lazy state

  • How it works: State is fetched on-demand on get calls from the Restate Server
  • Benefits: Reduces initial request size and memory usage
  • Setup: Enable lazy state in the service or handler configuration
  • Best for: Large state objects that aren’t needed in every handler execution