Applicability
When to Use
✓When you need a complete audit trail of all changes
✓When different views of the same data are needed
✓When undo/redo functionality is required
Overview
How It Works
Event Sourcing stores every state change as an immutable event in a database via MCP. Instead of storing current state, you store the sequence of events that led to it. The PostgreSQL MCP Server stores events, while other MCP servers can subscribe to the event stream and build their own materialized views.
In an MCP architecture, the agent acts as the command handler: it validates commands, produces events, and stores them. Read models are built by replaying events through projection functions. This gives you a complete audit trail and the ability to rebuild any view of the data at any point in time.
Implementation
Code Example
typescript
async function handleCommand(command) {
const currentState = await rebuildState(command.aggregateId);
const events = processCommand(currentState, command);
for (const event of events) {
await postgres.query(
"INSERT INTO events (aggregate_id, type, data, version) VALUES ($1, $2, $3, $4)",
[command.aggregateId, event.type, JSON.stringify(event.data), event.version]
);
}
// Update read models
for (const event of events) await updateProjections(event);
}
async function rebuildState(aggregateId) {
const events = await postgres.query("SELECT * FROM events WHERE aggregate_id=$1 ORDER BY version", [aggregateId]);
return events.rows.reduce((state, event) => applyEvent(state, event), {});
}Quick Info
Categorymessaging
ComplexityHard