Struct NodeMetadata 

pub struct NodeMetadata {
    pub defer: bool,
    pub metadata: Option<HashMap<String, Value>>,
    pub destinations: Option<Vec<String>>,
    pub retry_policies: Vec<RetryPolicy>,
    pub error_handler: Option<String>,
    pub timeout_policies: Vec<TimeoutPolicy>,
    pub circuit_breaker: Option<CircuitBreakerConfig>,
    pub fallback_node: Option<String>,
}

Metadata stored for each node during graph construction

Contains configuration options that affect node execution behavior. The actual defer/retry behavior is implemented by the Pregel engine.

Fields

defer: bool

Whether this node’s execution should be deferred

metadata: Option<HashMap<String, Value>>

User-defined metadata for this node

destinations: Option<Vec<String>>

Optional list of destination node names

retry_policies: Vec<RetryPolicy>

Retry policies for this node

error_handler: Option<String>

Optional error handler node name for engine-level error recovery.

When a task executing this node fails, the Pregel engine checks this field. If set, the engine creates a recovery task targeting the named handler node instead of canceling all remaining tasks. The error handler node receives a [NodeError] and returns a [Command] whose update is applied normally.

timeout_policies: Vec<TimeoutPolicy>

Timeout policies for this node, applied by the Pregel engine during superstep execution. The timeout wraps the entire execution (including retry attempts when a retry policy is also configured).

circuit_breaker: Option<CircuitBreakerConfig>

Optional circuit breaker configuration for this node.

When configured, the Pregel engine tracks consecutive failures and opens the circuit after the threshold is reached, preventing further execution attempts until the cooldown period expires.

fallback_node: Option<String>

Optional fallback node name for graceful degradation.

When a task executing this node fails (after retries), the Pregel engine creates a recovery task targeting the fallback node instead of propagating the error. The fallback node receives the same state as the failed node and its output is applied normally.

Priority order for failure handling:

1. fallback_node (if set)
2. error_handler (if set)
3. Cancel remaining tasks

Trait Implementations

impl Clone for NodeMetadata

fn clone(&self) -> NodeMetadata

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for NodeMetadata

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

Formats the value using the given formatter.

impl Default for NodeMetadata

fn default() -> NodeMetadata

Returns the “default value” for a type.