Cephalon.EventSourcing.Qdrant

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Maturity: M1 · Ownership: provider-managed · Family: event-sourcing · See audit, matrix.

Cephalon.EventSourcing.Qdrant is the Qdrant vector-store event-store provider for Cephalon, implementing IEventStore against a Qdrant vector collection using payload-only indexing with 1-dimensional dummy vectors.

What it owns

implements IEventStore backed by a Qdrant vector collection
stores each domain event as a point with a 1-dimensional dummy vector ([0.0f]) and all event metadata in payload fields — vector capabilities remain available for future semantic search scenarios
derives compound point IDs from {streamId}:{streamVersion} via SHA-256 hash (first 16 bytes) for structural uniqueness
enforces optimistic concurrency via a pre-append GetVersionAsync check followed by UpsertAsync
creates the collection and payload indexes on stream_id (keyword) and stream_version (integer) on first use
reads streams via ScrollAsync with payload filter on stream_id and stream_version >= fromVersion, sorted in memory by stream_version
serializes event payloads with System.Text.Json
reconstructs domain events by resolving Type.GetType(AssemblyQualifiedName) and deserializing via JsonSerializer

Main surfaces

QdrantEventEntry.cs — plain-object representation of a single event stored in a Qdrant point
QdrantEventStore.cs — IEventStore implementation
Hosting/QdrantEventSourcingServiceCollectionExtensions.cs — AddCephalonQdrantEventSourcing registration

How it fits

Cephalon.EventSourcing.Qdrant plugs into the IEventStore contract owned by Cephalon.EventSourcing. Application code depends only on IEventStore — swapping providers requires only a registration change. The Qdrant client connects lazily on first operation, so DI resolution does not require a live Qdrant server.

Registration

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services.AddCephalonQdrantEventSourcing(
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    host: "localhost",
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    port: 6334,
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    collectionName: "event-streams");

Point schema (event-streams collection)

Payload field	Type	Notes
`stream_id`	keyword	Stream identifier; indexed for efficient scroll filtering
`stream_version`	integer	Monotonically increasing version; indexed for range filtering
`event_type`	keyword	Assembly-qualified CLR type name
`payload`	keyword	JSON-serialized event body
`occurred_at_utc`	keyword	ISO 8601 UTC timestamp when the domain event occurred
`appended_at_utc`	keyword	ISO 8601 UTC timestamp when the event was appended

Point ID is derived from SHA-256({streamId}:{streamVersion})[0..16] as a UUID.

Optimistic concurrency

AppendAsync reads the current stream version before upserting events. If the actual version does not match expectedVersion, an EventStreamConcurrencyException is thrown before any points are upserted. Concurrent writers that both observe the same expectedVersion will both proceed to upsert — the compound point-ID hash provides a structural safeguard but full atomicity is not guaranteed. This is consistent with the ClickHouse and OpenSearch provider approaches.

Not shipped in this slice

This provider intentionally does not claim:

semantic similarity search over event payloads
event projections or read-model maintenance
snapshotting or stream archival
multi-collection event streams
Qdrant gRPC streaming for incremental replay