Subtitle:
Directed acyclic graphs for representing conversation history in Matrix
Core Idea:
Event graphs in Matrix are directed acyclic graphs (DAGs) that store and order all events exchanged within a room, providing a partially ordered chronological history that can handle concurrent events from multiple servers.
Key Principles:
- Directed Acyclic Structure:
- Events point to their parent events, creating a graph with no cycles that flows in one direction (forward in time).
- Event Depth:
- Each event has a depth value strictly greater than its parents to maintain chronological ordering.
- Partial Ordering:
- Events may have multiple parent events when homeservers send messages concurrently.
Why It Matters:
- Distributed Consistency:
- Enables eventual consistency across distributed servers without requiring real-time coordination.
- Conflict Resolution:
- Provides a clear mechanism for resolving concurrent messages from different servers.
- History Preservation:
- Maintains a complete, immutable record of all communication within a room.
How to Implement:
- Event Creation:
- When sending an event, identify the current "frontier" events that have no successors.
- Parent References:
- Include references to these parent events in the new event's metadata.
- Depth Assignment:
- Assign a depth value that's greater than the maximum depth of all parent events.
Example:
- Scenario:
- Two users on different homeservers send messages simultaneously to a Matrix room.
- Application:
- Each homeserver creates an event with the same parent (the previous message), resulting in two events with the same parent.
- Result:
- The next message will reference both as parents, creating a graph that merges these parallel conversation branches.
Connections:
- Related Concepts:
- Matrix Protocol: The communication protocol using event graphs
- Room Structure in Matrix: The container for event graphs
- Broader Concepts:
- Directed Acyclic Graphs: Mathematical structure used in distributed systems
- Eventual Consistency: Data synchronization model prioritizing availability over immediate consistency
References:
- Primary Source:
- Matrix Specification: Room Version section
- Additional Resources:
- Matrix Architecture documentation
- Matrix State Resolution Algorithm documentation
Tags:
#matrix #eventgraphs #dag #distributedcomputing #messaging #consistency
Connections:
Sources:
- From: Matrix Specification