beamologist

ExESDB - a BEAM-Native Event Store

Event Sourcing with CQRS is a technique for building applications that are based on an immutable log of events, which makes it ideal for building concurrent, distributed systems.

Though it is gaining popularity, the number of options for storing these events is limited and require specialized services like Kurrent (aka Greg’s EventStore) or AxonIQ.
One of the strong-points of the BEAM is, that it comes ‘batteries included’: there are BEAM-native libraries for many common tasks, like: storage, pub/sub, caching, logging, telemetry, etc.

ExESDB is an attempt to create a BEAM-native Event Store, building further upon the Khepri library, which in turn builds upon the Ra library.

On the roadmap:

integration with pg2 and Phoenix.PubSub for side effects (i.e. read model projections)
interfacing with the Commanded library
leverage Partisan for clustering

Check it out on Hex or GitHub:

https://github.com/beam-campus/ex-esdb

18 comments

#library #event-sourcing #cqrs

20 1546 18

2025-07-15 17:32:01 UTC

First Post!

Eiji

Interesting idea. I’m curious about plans for the commanded support.

So you plan to create an implementation for the Commanded.EventStore.Adapter behaviour, right? In that case it would be interesting to hear about a key differences between your library and PostgreSQL-based Elixir EventStore / EventStoreDB.

I guess it would be something like In memory event store, but for production. That should give us less required environment dependencies which is great. Are there any other pros for that like speed or security?

What kind of serializer would be needed? Would it work with the Elixir structs as-is or we would still need to use a JSON serializer?

Suppose some project already uses other adapter. Would that require some extra steps for migrating data?

Post #1

Most Liked

beamologist

ExESDB v0.1.0 available!
I am proud to announce that the first useful release of ExESDB is now available as v0.1.0! This release comes with an adapter for the fantastic Commanded Library AND a Phoenix LiveView demo app. Feel free to check it out

On Hex:

On Github

DEMO Video
Comments and Feedback most welcome!

Post #7

beamologist

Hi Eiji,

It has taken me a few months to finish things up (but then, what is ‘finished’, right?) but meanwhile, the distributed store is there, a HA proxy is there and…the Commanded adapter is there, too!
It is said that the proof of the pudding is in the eating, so the adapter is being developed and tested in conjunction with a working Phoenix LiveView application: an event-sourced demo app that mimics a dashboard for regulating greenhouses. All data (events) is stored in ExESDB, while Cachex is used for read models, thus creating a true BEAM-only application without the need of any external services like EventStoreDB or PostgreSQL.

I must confess, it feels a little liberating, being able to just spin up a few containers and not having to worry about connectivity with other backend components.

Also, since we remain in the same ecosystem, there is no need to worry about (or waste processing power with) serialization. Serialization will only become a topic if and when we decide to create API’s for clients in other languages..

Post #8

beamologist

Hi Tomasz,
Thank you for your feedback.
Next to the advantages you already mentioned (speed, security, no need for extra serialization - events are indeed stored as Erlang terms), I’d like to add the capability to deploy event sourced services as a self-contained BEAM-native release to the edge. This would allow us to leverage for instance The Nerves Project for deployment.
I am also looking in to https://bondy.io for scenarios where you could have 10E+N nodes in the network.
Much of my past work revolved around decentralized and autonomous systems (think Parking Facilities, Vehicles, Agricultural automation, Logistics etc), often in a “spotty” environment, where nodes aren’t always connected. Such systems benefit little from SaaS solutions, if the network is not available. That space could be considered my main motivator to build a BEAM-native event store: as few dependencies on 3rd party services as possible.

The reason for implementing the Commanded Adapter is simple: it is the de-facto event sourcing standard for the BEAM and is as far as I am concerned, feature complete.

When it comes to migrating data from existing stores, I’d argue that’s quite easy, barely an inconvenience: replay the old store and project into the new.
So, indeed: highest points on the agenda are:

1, have Kherpi triggers throw seen events on pg2 (for projections etc…)
2. Dynamic Clustering via Partisan
3. Commanded Adapter
4. Monitoring/Telemetry
…

Post #2