README.md

EventHorizon Scylla

Build scalable eventstore with scylla

Features

Multi bounded-context

Take advantage of NoSQL. We can use event store as a single source of truth throughout all contexts in your domain without scaling issues.

Partitioning vs. Sharding

To improve query performance, the data is partitioned and sharded based on the bounded_context, aggregate_id, and aggregate_type columns, also sorted by event_version column; this means that events belonging to one aggregate always live in a specific node.

Transaction

By using LTW (Lightweight transaction), consistency level, and batch query, we archive the Atomicity property on a single partition.

Snapshot

Snapshot logic is triggered when the aggregate store saves or loads events. Furthermore, you can customize the snapshot strategy.

Compaction

Event_store table uses Size-tiered compaction strategy to improve read speed.

Aggregate_snapshot table uses Leveled compaction strategy to reduce disk size and improve read speed.

Installation

go get github.com/datdao/eh-scylla

Usage

Run migration script

CREATE KEYSPACE event_sourcing WITH replication = {'class': 'NetworkTopologyStrategy', 'replication_factor' : 3};

CREATE TABLE event_store (bounded_context varchar, aggregate_id uuid, aggregate_type varchar, event_id uuid, event_type varchar, event_version int, event_data varchar, event_timestamp timestamp, event_metadata varchar, PRIMARY KEY ((bounded_context, aggregate_id, aggregate_type), event_version));

CREATE TABLE aggregate_snapshot (bounded_context varchar, aggregate_id uuid, aggregate_type varchar, snapshot_data varchar, snapshot_version int, snapshot_timestamp timestamp, snapshot_metadata varchar, PRIMARY KEY ((bounded_context, aggregate_id, aggregate_type))) WITH compaction = { 'class' : 'LeveledCompactionStrategy' };

Create AggregateStore

hosts := strings.Split(os.Getenv("SCYLLA_HOSTS"), ",")
username := os.Getenv("SCYLLA_USERNAME")
password := os.Getenv("SCYLLA_PASSWORD")
hostSelectionPolicy := os.Getenv("SCYLLA_HOSTSELECTIONPOLICY")

var cluster = gocql.NewCluster(hosts...)
cluster.Authenticator = gocql.PasswordAuthenticator{Username: username, Password: password}
cluster.PoolConfig.HostSelectionPolicy = gocql.DCAwareRoundRobinPolicy(hostSelectionPolicy)
cluster.Keyspace = "event_sourcing"
cluster.Consistency = gocql.Quorum

// Create gocql cluster.
session, err := cluster.CreateSession()
if err != nil {
    panic(err)
}

// Create aggreagate store
aggStore, err := ehScylla.NewAggregateStoreWithBoundedContext(session, "order", nil, nil)
if err != nil {
    panic(err)
}

Custom Snapshot strategy

var StrategySnapshotCustom = func(aggregate eh.Aggregate) bool {
	return aggregate.EntityID().Version()%20 == 0
}

ehScylla.NewAggregateStoreWithBoundedContext(session, "order", nil, StrategySnapshotCustom)