---
title: "Production Append-Only Event Store with Real-Time CQRS Projections | Distributed Systems Architecture Canon"
description: "Immutable event store recording domain facts as append-only streams, asynchronously projecting real-time materialized read models into optimized query datastores."
image: "https://tinycto.tv/assets/distributed-systems/distributed_systems_architectures_og.jpg"
canonicalUrl: "https://tinycto.tv/distributed-systems/architectures/cqrs-event-store-materialized-views"
locale: "en"
---

# Production Append-Only Event Store with Real-Time CQRS Projections (`arch-cqrs-event-store-materialized-views`)

> **Architectural Pillar**: EVENT_SOURCING_CQRS | **Archetype**: TRANSACTIONAL_OUTBOX_CDC
> **PACELC**: PA/EL | **Consensus Protocol**: None

Immutable event store recording domain facts as append-only streams, asynchronously projecting real-time materialized read models into optimized query datastores.

### 3 Maturity Target Configurations

#### 1. Initial Target: 3,000 events/sec

- **Guarantees**: Eventual Consistency (Projection Lag < 500ms)
- **Infrastructure Topology**: Single PostgreSQL instance with an append-only `events` table and an optimistic concurrency version column.
- **Operational Trade-Off**: Event log growth requires active table partitioning or table bloat slows sequential writes.

#### 2. Scaled Target: 45,000 events/sec

- **Guarantees**: Strict Optimistic Concurrency + Real-time Streaming Projections
- **Infrastructure Topology**: 3-node EventStoreDB cluster paired with Kafka connect projections feeding Elasticsearch read models.
- **Operational Trade-Off**: Event schema evolution requires strict upcasters and contract testing.

#### 3. Ultra-Scale Target: 400,000 events/sec

- **Guarantees**: Sub-10ms Global Read Projections with CQRS Snapshot Compaction
- **Infrastructure Topology**: Apache Flink streaming cluster aggregating millions of raw events per second into in-memory read models.
- **Operational Trade-Off**: Flink checkpoint storage operations and state recovery times during worker crashes.

### Handled Failure Modes

- `DS-FAIL-02: Dual-Write Mutation Drift`
- `DS-FAIL-10: Out-of-Order CDC Ingestion`
- `DS-FAIL-18: Event Sourcing Upcaster Failure`


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