Enum StateBackendConfig 

pub enum StateBackendConfig {
    InProcess {
        vnode_capacity: u32,
    },
    Local {
        path: PathBuf,
        instance_id: String,
        vnode_capacity: u32,
    },
    ObjectStore {
        url: String,
        storage: StorageOptions,
        instance_id: String,
        vnode_capacity: u32,
        vnodes: Option<Vec<u32>>,
        merger_instance: Option<String>,
        discovery: DiscoveryMode,
        seed_peers: Vec<String>,
    },
}

Tagged-union config that selects the runtime StateBackend.

See module docs for the five deployment shapes.

Variants

InProcess

Non-durable in-process backend. The default.

Fields

vnode_capacity: u32

Number of vnodes the backend should size for.

Local

Durable single-node backend on a local filesystem path. Shorthand for an object_store backend with a file:// URL.

Fields

path: PathBuf

Filesystem root for state.

instance_id: String

Node identity (written into epoch commit markers for audit).

vnode_capacity: u32

Number of vnodes the backend should size for.

ObjectStore

Durable shared-state backend on S3 / GCS / Azure. Used by all distributed-embedded and cluster modes.

Fields

url: String

Object store URL: s3://bucket/prefix, gs://bucket/prefix, etc.

storage: StorageOptions

Cloud credentials/config overrides (e.g. endpoint, aws_access_key_id), same keys as [checkpoint.storage]. Anything absent falls back to the provider’s standard env vars (AWS_ACCESS_KEY_ID, …).

instance_id: String

This node’s identity. Written into epoch manifests and used by the assignment-version fence to reject stale writes.

vnode_capacity: u32

Number of vnodes the backend should size for.

vnodes: Option<Vec<u32>>

Static vnode subset for this instance. None means “all vnodes” (useful for the merger instance or for dynamic mode).

merger_instance: Option<String>

Optional merger instance — the node that fans in partials for sink emission. Only meaningful in static mode.

discovery: DiscoveryMode

Discovery strategy: static assignment or chitchat gossip.

seed_peers: Vec<String>

Seed peers for dynamic discovery.

Implementations

impl StateBackendConfig

pub fn in_process() -> Self

Builder: embedded library, single process.

pub fn local(path: impl Into<PathBuf>) -> Self

Builder: single-node durable state on the local filesystem.

pub fn object_store( url: impl Into<String>, instance_id: impl Into<String>, ) -> Self

Builder: distributed-embedded over an object store, static mode. Credentials resolve from the provider’s standard env vars; use the storage config field for explicit overrides.

pub async fn build( &self, ) -> Result<Arc<dyn StateBackend>, StateBackendBuildError>

Instantiate the runtime backend.

Declared async because backends added in later iterations (object store, distributed) need to perform async setup. The in-process path completes synchronously today; callers must still .await for forward-compatibility.

Errors

• StateBackendBuildError::Store for a bad URL, a scheme whose feature flag (aws/gcs/azure) is not compiled in, or cloud-client construction failure.
• StateBackendBuildError::Io on filesystem setup.

pub fn local_storage_dir(&self) -> Option<&Path>

Filesystem path for durable state, if any. Returns None for non-filesystem backends.

pub fn build_object_store( &self, ) -> Result<Option<Arc<dyn ObjectStore>>, StateBackendBuildError>

Build the underlying object_store handle (if any) so callers that need to share the same store — e.g. an AssignmentSnapshotStore alongside the state backend — can avoid re-parsing the URL. None for InProcess.

Errors

Same failure modes as Self::build.

pub fn is_durable(&self) -> bool

Returns true if this backend persists state across process restarts.

pub fn vnode_capacity(&self) -> u32

Number of vnodes this backend is sized for.

Trait Implementations

impl Clone for StateBackendConfig

fn clone(&self) -> StateBackendConfig

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for StateBackendConfig

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for StateBackendConfig

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for StateBackendConfig

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for StateBackendConfig

impl PartialEq for StateBackendConfig

fn eq(&self, other: &StateBackendConfig) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for StateBackendConfig