Module subscription 

Reactive Subscription System

Foundation types for the push-based subscription system that delivers change events from materialized views and streaming queries to consumers.

Architecture

The subscription system spans all three rings:

• Ring 0: NotificationRef — zero-allocation, cache-line-aligned notification
• Ring 1: ChangeEvent — data delivery with Arc<RecordBatch> payloads
• Ring 2: Subscription lifecycle management

Types

• EventType — Discriminant for change event kinds (Insert/Delete/Update/Watermark/Snapshot)
• NotificationRef — 64-byte cache-aligned Ring 0 notification slot
• ChangeEvent — Rich change event with Arrow data for Ring 1 delivery
• ChangeEventBatch — Coalesced batch of change events

Structs

BackpressureController

Per-subscription backpressure controller.

BatchConfig

Configuration for notification batching.

CallbackSubscriptionHandle

Handle for a callback-based subscription.

ChangeEventBatch

A batch of change events for coalesced delivery to subscribers.

ChangeEventResultStream

Async stream that also yields lag errors.

ChangeEventStream

Async stream wrapper for push subscriptions.

DemandBackpressure

Demand-based backpressure (Reactive Streams request(n) model).

DemandHandle

Handle given to the subscriber to request more events.

DispatcherConfig

Configuration for the SubscriptionDispatcher.

DispatcherMetrics

Atomic counters for monitoring the dispatcher.

NotificationBatcher

Accumulates events per source and flushes as batches.

NotificationHub

Manages notification slots and the SPSC ring for a single reactor core.

NotificationRef

Zero-allocation notification reference for Ring 0.

NotificationRing

Lock-free SPSC ring buffer carrying NotificationRef from Ring 0 to Ring 1.

NotificationSlot

Per-source notification slot with atomic sequence counter.

PushSubscription

A push-based subscription handle.

StringInternTable

Intern table for string values used in Ring 0 predicates.

SubscriptionConfig

Configuration for a subscription.

SubscriptionDispatcher

Ring 1 dispatcher that routes notifications to subscriber channels.

SubscriptionEntry

A registered subscription entry with state, config, channel, and metrics.

SubscriptionFilter

Compiled subscription filter.

SubscriptionId

Unique subscription identifier.

SubscriptionMetrics

Point-in-time metrics snapshot for a subscription.

SubscriptionRegistry

Registry managing all active subscriptions.

Enums

BackpressureStrategy

Strategy applied when a subscription’s channel buffer is full.

ChangeEvent

A change event carrying Arrow data for subscriber delivery.

EventType

Discriminant for change event kinds.

FilterCompileError

Filter compilation errors.

PushSubscriptionError

Errors from push subscription operations.

Ring0Predicate

Ring 0 predicate (must be zero-allocation, < 50ns).

Ring1Predicate

Ring 1 predicate (can allocate, evaluated in Ring 1 dispatcher).

ScalarValue

Scalar value for Ring 0 predicate comparison.

SubscriptionState

Lifecycle state of a subscription.

Traits

NotificationDataSource

Resolves a NotificationRef into a full ChangeEvent.

SubscriptionCallback

Callback trait for push-based subscriptions.

Functions

compile_filter

Compiles a filter expression into Ring 0 and Ring 1 predicates.

subscribe_callback

Creates a callback-based subscription.

subscribe_fn

Creates a closure-based subscription (convenience wrapper).

subscribe_stream

Creates an async Stream subscription.

subscribe_stream_with_errors

Creates an async Stream that also yields errors.