SierraDB

A high-performance, distributed event store designed for scalable event sourcing applications

SierraDB is a modern, horizontally-scalable database specifically built for event sourcing workloads. It combines the simplicity of Redis protocol compatibility with the distributed architecture principles of Cassandra/ScyllaDB, providing developers with a powerful foundation for building event-driven systems.

📖 Learn More

Want to understand how SierraDB works under the hood? Read the detailed blog post: Building SierraDB: A Distributed Event Store Built in Rust

The post covers the architecture decisions, watermark system for consistency, distributed consensus, and the journey of building an event store from scratch.

🚀 Try it in 30 seconds

Get SierraDB running with Docker and start storing events immediately:

# Start SierraDB
docker run -p 9090:9090 tqwewe/sierradb

# In another terminal, use redis-cli to interact with SierraDB
redis-cli -p 9090

# Append some events to a user stream
EAPPEND user-123 UserRegistered EXPECTED_VERSION empty PAYLOAD '{"email":"[email protected]","name":"Alice"}'
EAPPEND user-123 EmailVerified EXPECTED_VERSION 0 PAYLOAD '{"timestamp":"2024-10-18T10:30:00Z"}'
EAPPEND user-123 ProfileUpdated EXPECTED_VERSION 1 PAYLOAD '{"bio":"Software engineer"}'

# Read all events from the stream
ESCAN user-123 - +

# Get the current version of the stream
ESVER user-123

# Subscribe to new events (will stream in real-time)
ESUB user-123 FROM LATEST

That's it! You're now running a distributed event store and can append/read events using any Redis client.

Quick Start

Using Docker (Recommended)

# Run with persistent data
docker run -p 9090:9090 -v ./data:/app/data tqwewe/sierradb

Install with Cargo

cargo install sierradb-server
sierradb --dir ./data --client-address 0.0.0.0:9090

Basic Event Operations

# Connect with any Redis client
redis-cli -p 9090

# Append events to streams
EAPPEND order-456 OrderCreated EXPECTED_VERSION empty PAYLOAD '{"total":99.99,"items":["laptop"]}'

# Read events back
ESCAN orders - + COUNT 100

# Subscribe to real-time events
ESUB orders FROM LATEST

Using with Redis Clients

Since SierraDB uses the RESP3 protocol, you can also connect with any Redis-compatible client:

import redis

# Connect to SierraDB
client = redis.Redis(host='localhost', port=9090, protocol=3)

# Append an event (use 'empty' for new streams, or a version number for existing ones)
result = client.execute_command('EAPPEND', 'user-123', 'UserCreated',
                               'EXPECTED_VERSION', 'empty',
                               'PAYLOAD', '{"name":"John","email":"[email protected]"}')

# Read events from stream
events = client.execute_command('ESCAN', 'user-123', '-', '+', 'COUNT', '100')

Key Features

• Redis Protocol Compatible - Uses RESP3 protocol, making it compatible with existing Redis clients and tools
• Horizontally Scalable - Distributed architecture that scales across multiple nodes with configurable replication
• High Performance - Optimized for event sourcing with consistent write performance regardless of database size
• Real-time Subscriptions - Seamless transition from historical events to live streaming for projections and event handlers
• Event Sourcing Optimized - Purpose-built for append-only event patterns with strong ordering guarantees
• Data Integrity - CRC32C checksums ensure corruption detection with automatic recovery capabilities
• Actively Developed - Under active development with extensive testing and stability improvements

Architecture Overview

SierraDB organizes data using a three-tier hierarchy designed for optimal performance and scalability:

Buckets and Partitions

• Default Configuration: 4 buckets containing 32 partitions (8 partitions per bucket)
• Scalability: Can be scaled up across many nodes for virtually unlimited horizontal performance
• Distribution: Events are distributed across partitions using consistent hashing of partition keys

Segmented Storage

• Segment Files: Events are written to segment files that are sealed at 256MB (configurable)
• Consistent Performance: New segments ensure write performance remains constant regardless of database size
• Parallel Processing: Writes within a partition are sequential, but parallel across different partitions

Event Ordering Guarantees

• Partition Sequences: Gapless monotonic sequence numbers within each partition
• Stream Versions: Gapless monotonic version numbers within each stream
• Consistency: Events within the same partition maintain strict ordering while allowing parallelism across partitions

Performance Characteristics

SierraDB is optimized for three primary read patterns:

1. Event Lookup by ID - Fast UUID-based event retrieval using event indexes
2. Stream Scanning - Efficient sequential reading of events within a stream using stream indexes
3. Partition Scanning - High-throughput scanning of events within a partition using partition indexes

Each segment file is accompanied by specialized index files and bloom filters for maximum query performance.

Distributed Architecture

SierraDB operates as a distributed cluster similar to Cassandra/ScyllaDB:

• Cluster Coordination - Automatic node discovery and coordination using libp2p and optional mDNS
• Replication Factor - Configurable data replication (defaults to min(node_count, 3))
• Fault Tolerance - Automatic failover and data recovery across cluster nodes
• Consistent Hashing - Automatic data distribution and rebalancing

Real-time Subscriptions

One of SierraDB's most powerful features is its subscription system, designed specifically for event sourcing projections:

• Historical + Live: Subscriptions start from any point in history and automatically transition to live events
• Guaranteed Delivery: Events are delivered in order with acknowledgment tracking
• Multiple Stream Types: Subscribe to individual streams, partitions, or combinations
• Backpressure Handling: Configurable windowing prevents overwhelmed consumers

Perfect for building:

• Event sourcing projections that need to catch up from the beginning
• Real-time event handlers that process new events as they arrive
• Read models that require both historical rebuild and live updates

Configuration

SierraDB offers extensive configuration options. Key settings include:

[append]
strict_versioning = true     # Require explicit EXPECTED_VERSION (empty or number)

[bucket]
count = 4                    # Number of buckets

[partition]
count = 32                   # Number of partitions (8 per bucket by default)

[segment]
size_bytes = 268435456       # Segment size in bytes (256MB default)

[replication]
factor = 3                   # Data replication factor
buffer_size = 1000           # Replication buffer size
buffer_timeout_ms = 8000     # Buffer timeout

[network]
client_address = "0.0.0.0:9090"           # Client connection address
cluster_address = "/ip4/0.0.0.0/tcp/0"   # Inter-node communication

[threads]
read = 8                     # Read thread pool size
write = 4                    # Write thread pool size

See crates/sierradb-server/src/config.rs for the complete configuration reference.

Supported Operations

SierraDB implements a comprehensive set of RESP3 commands for event operations:

Core Event Operations

EAPPEND - Append Event to Stream

Append an event to a stream with expected version control.

Note: By default, EXPECTED_VERSION must be empty (for new streams) or a specific version number. To allow any or exists, set append.strict_versioning = false in your configuration.

Syntax:

EAPPEND <stream_id> <event_name> [EVENT_ID <event_id>] [PARTITION_KEY <partition_key>] [EXPECTED_VERSION <version>] [TIMESTAMP <timestamp>] [PAYLOAD <payload>] [METADATA <metadata>]

Parameters:

• stream_id - Stream identifier to append the event to
• event_name - Name/type of the event
• event_id (optional) - UUID for the event (auto-generated if not provided)
• partition_key (optional) - UUID to determine event partitioning
• expected_version - Expected stream version (empty for new streams, or version number)
• timestamp (optional) - Event timestamp in milliseconds
• payload (optional) - Event payload data
• metadata (optional) - Event metadata

Examples:

EAPPEND my-stream UserCreated EXPECTED_VERSION empty PAYLOAD '{"name":"john"}' METADATA '{"source":"api"}'
EAPPEND orders OrderPlaced EXPECTED_VERSION 5 PAYLOAD '{"order_id":"12345"}'

EMAPPEND - Multi-Stream Transactional Append

Append multiple events across different streams within the same partition atomically.

Syntax:

EMAPPEND <partition_key> <stream_id1> <event_name1> [EVENT_ID <event_id1>] [EXPECTED_VERSION <version1>] [TIMESTAMP <timestamp>] [PAYLOAD <payload1>] [METADATA <metadata1>] [<stream_id2> <event_name2> ...]

Parameters:

• partition_key - UUID that determines which partition all events will be written to
• For each event: stream_id, event_name, and optional EVENT_ID, EXPECTED_VERSION, TIMESTAMP, PAYLOAD, METADATA

Examples:

EMAPPEND 550e8400-e29b-41d4-a716-446655440000 stream1 EventA EXPECTED_VERSION empty PAYLOAD '{"data":"value1"}' stream2 EventB EXPECTED_VERSION 3 PAYLOAD '{"data":"value2"}'

Note: All events succeed or fail together as a single atomic transaction.

EGET - Get Event by ID

Retrieve an event by its unique identifier.

Syntax:

EGET <event_id>

Parameters:

• event_id - UUID of the event to retrieve

Examples:

EGET 550e8400-e29b-41d4-a716-446655440000

ESCAN - Scan Stream Events

Scan events in a stream by version range.

Syntax:

ESCAN <stream_id> <start_version> <end_version> [PARTITION_KEY <partition_key>] [COUNT <count>]

Parameters:

• stream_id - Stream identifier to scan
• start_version - Starting version number (use "-" for beginning)
• end_version - Ending version number (use "+" for end, or specific number)
• partition_key (optional) - UUID to scan specific partition
• count (optional) - Maximum number of events to return

Examples:

ESCAN my-stream 0 100 COUNT 50
ESCAN my-stream - + PARTITION_KEY 550e8400-e29b-41d4-a716-446655440000

Stream Operations

ESVER - Get Stream Version

Get the current version number for a stream.

Syntax:

ESVER <stream_id> [PARTITION_KEY <partition_key>]

Parameters:

• stream_id - Stream identifier to get version for
• partition_key (optional) - UUID to check specific partition

Examples:

ESVER my-stream
ESVER my-stream PARTITION_KEY 550e8400-e29b-41d4-a716-446655440000

ESUB - Subscribe to Stream Events

Subscribe to events from one or more streams with real-time delivery.

Syntax:

# Single stream
ESUB <stream_id> [PARTITION_KEY <partition_key>] [FROM <version>] [WINDOW <size>]

# Multiple streams  
ESUB <stream_id_1> [PARTITION_KEY <pk_1>] <stream_id_2> [PARTITION_KEY <pk_2>] ... [FROM LATEST | FROM <version> | FROM MAP <stream>=<ver>...] [WINDOW <size>]

Parameters:

• stream_id - Stream identifier(s) to subscribe to
• partition_key (optional) - UUID for specific partition
• FROM (optional) - Starting position (LATEST, version number, or MAP for per-stream positions)
• WINDOW (optional) - Maximum number of unacknowledged events

Examples:

ESUB user-123                                         # Single stream, latest, no window
ESUB user-123 WINDOW 100                              # Single stream, latest, window 100  
ESUB user-123 FROM 50 WINDOW 100                      # Single stream, from version 50
ESUB user-1 user-2 user-3 FROM MAP user-1=10 user-2=20 user-3=30 WINDOW 50

Note: Establishes a persistent connection for real-time event delivery.

Partition Operations

EPSCAN - Scan Partition Events

Scan events in a partition by sequence number range.

Syntax:

EPSCAN <partition> <start_sequence> <end_sequence> [COUNT <count>]

Parameters:

• partition - Partition selector (partition ID 0-65535 or UUID key)
• start_sequence - Starting sequence number (use "-" for beginning)
• end_sequence - Ending sequence number (use "+" for end, or specific number)
• count (optional) - Maximum number of events to return

Examples:

EPSCAN 42 100 200 COUNT 50
EPSCAN 550e8400-e29b-41d4-a716-446655440000 - + COUNT 100

EPSEQ - Get Partition Sequence

Get the current sequence number for a partition.

Syntax:

EPSEQ <partition>

Parameters:

• partition - Partition selector (partition ID 0-65535 or UUID key)

Examples:

EPSEQ 42
EPSEQ 550e8400-e29b-41d4-a716-446655440000

EPSUB - Subscribe to Partition Events

Subscribe to events from one or more partitions with real-time delivery.

Syntax:

# All partitions
EPSUB * [FROM LATEST | FROM <sequence> | FROM MAP <p1>=<s1> <p2>=<s2>... [DEFAULT <seq>]] [WINDOW <size>]

# Single partition
EPSUB <partition_id> [FROM <sequence>] [WINDOW <size>]

# Multiple partitions
EPSUB <p1>,<p2>,<p3> [FROM LATEST | FROM <sequence> | FROM MAP <p1>=<s1> <p2>=<s2>... [DEFAULT <seq>]] [WINDOW <size>]

Parameters:

• partition_id - Partition identifier(s) (* for all, comma-separated list for multiple)
• FROM (optional) - Starting position (LATEST, sequence number, or MAP for per-partition positions)
• WINDOW (optional) - Maximum number of unacknowledged events

Examples:

EPSUB *                                               # All partitions, latest
EPSUB * WINDOW 100                                    # All partitions, latest, window 100
EPSUB * FROM 1000 WINDOW 100                          # All partitions, from seq 1000  
EPSUB 5 FROM 100 WINDOW 50                            # Partition 5, from seq 100
EPSUB 1,2,3 FROM MAP 1=100 2=200 DEFAULT 0 WINDOW 500

Note: Establishes a persistent connection for real-time event delivery.

Subscription Management

EACK - Acknowledge Events

Acknowledge events up to a cursor for a subscription.

Syntax:

EACK <subscription_id> <sequence_or_version>

Parameters:

• subscription_id - UUID of the subscription
• sequence_or_version - Sequence or version number to acknowledge up to

Examples:

EACK 550e8400-e29b-41d4-a716-446655440000 1000

Note: Tells SierraDB that events up to the specified position have been processed successfully.

System Operations

HELLO - Protocol Handshake

Perform protocol handshake and retrieve server information.

Syntax:

HELLO <version>

Parameters:

• version - Protocol version (currently only 3 is supported)

Examples:

HELLO 3

Returns:

• server - Server name ("sierradb")
• version - Server version
• peer_id - Cluster peer ID
• num_partitions - Number of partitions

PING - Health Check

Simple health check and connectivity test.

Syntax:

PING

Returns: PONG

Examples:

PING

Data Integrity & Transactions

SierraDB ensures data reliability through multiple mechanisms:

• CRC32C Checksums: Every event includes integrity checksums to detect corruption
• Atomic Transactions: Events within the same partition can be written transactionally
• Corruption Recovery: Automatic detection and recovery from data corruption scenarios
• Graceful Shutdown Handling: Proper recovery even after sudden system shutdowns

Cluster Setup

For distributed deployments across multiple nodes:

# Node 1
sierradb --dir ./data1 --node-index 0 --node-count 3 --client-address 0.0.0.0:9090

# Node 2  
sierradb --dir ./data2 --node-index 1 --node-count 3 --client-address 0.0.0.0:9091

# Node 3
sierradb --dir ./data3 --node-index 2 --node-count 3 --client-address 0.0.0.0:9092

Embedded Usage

For Rust applications, SierraDB can be embedded directly using the core sierradb crate:

use std::time::{SystemTime, UNIX_EPOCH};
use sierradb::{Database, Transaction, NewEvent, StreamId};
use sierradb::id::{NAMESPACE_PARTITION_KEY, uuid_to_partition_hash, uuid_v7_with_partition_hash};
use sierradb_protocol::ExpectedVersion;
use uuid::Uuid;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Open database directly
    let db = Database::open("./data")?;
    
    // Create and append events
    let stream_id = StreamId::new("user-123")?;
    let partition_key = Uuid::new_v5(&NAMESPACE_PARTITION_KEY, stream_id.as_bytes());
    let partition_hash = uuid_to_partition_hash(partition_key);
    let partition_id = uuid_v7_with_partition_hash(partition_hash);
    let timestamp = SystemTime::now()
        .duration_since(UNIX_EPOCH)?
        .as_nanos() as u64;

    let transaction = Transaction::new(
        partition_key,
        partition_id,
        vec![NewEvent {
            event_id: Uuid::new_v4(),
            stream_id,
            stream_version: ExpectedVersion::Empty,
            event_name: "UserCreated".into(),
            timestamp,
            payload: br#"{"name":"john"}"#.to_vec(),
            metadata: vec![],
        }]
    )?;
    
    let result = db.append_events(transaction).await?;
    println!("Event appended with sequence: {}", result.first_partition_sequence);
    
    Ok(())
}

Using the Rust Client

SierraDB provides a native Rust client built on top of the redis crate with full type support for SierraDB commands and subscriptions:

use sierradb_client::{SierraClient, SierraAsyncClientExt, SierraMessage};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = SierraClient::connect("redis://localhost:9090").await?;
    
    // Append an event with type safety
    let options = EAppendOptions::new()
        .payload(br#"{"name":"john"}"#)
        .metadata(br#"{"source":"api"}"#);
    let result = client.eappend("user-123", "UserCreated", options)?;
    
    // Scan events from stream
    let events = client.escan("user-123", "-", None, Some(50))
        .execute()
        .await?;
    
    // Subscribe to real-time events
    let mut manager = client.subscription_manager().await?;
    let mut subscription = manager
        .subscribe_to_stream_from_version("user-123", 0)
        .await?;
    while let Some(msg) = subscription.next_message().await? {
        println!("Received event: {msg:?}");
    }
    
    Ok(())
}

Development Status

SierraDB is under active development and testing:

• Stability Testing: Extensive fuzzing campaigns ensure robustness under edge conditions
• Performance Validation: Consistent performance characteristics validated across various workloads
• Current Usage: Being used to build systems in development and testing environments
• Data Safety: Comprehensive corruption detection and recovery mechanisms implemented

Note: While SierraDB demonstrates strong stability in testing, it is not yet recommended for production use. The project is actively working toward production readiness.

Contributing

SierraDB is being prepared for public release. Contribution guidelines and development setup will be available once the repository is made public.

License

SierraDB is licensed under the Apache License 2.0. See the LICENSE file for details.

---

Ready to scale your event sourcing architecture? SierraDB provides the performance, reliability, and developer experience you need to build robust event-driven systems.