Best DB for chat

I would try

• scylla [0] for storing messages,
• postgres for storing user metadata (might replace with cockroach [1] for lolavailability, it’s definitely production ready, hit 1.0 a few weeks ago),
• elasticsearch for, well, searching through all those messages and users,
• prometheus 2.0-alpha [2] for collecting and storing metrics (2.0-alpha because stable is way too stable)

[0] http://www.scylladb.com
[1] https://www.cockroachlabs.com
[2] https://prometheus.io

Actually, even though cockroach is very nice, I might still stay with postgres because of postgis (might come in handy if you plan to support location sharing, “users nearby”, “boys from my hood” etc.).

Note: I’ve never written anything more complex than a “hello world.” So you should really just skip to the next answer.

How much traffic do you expect on it? I would keep it simple and stick to Postgres. It plays well with Ecto, widely used in the industry, better tooling, easy to setup, etc.

I’m sorry for answering your question with somewhat of a non-answer, but it has to be mentioned: A Little Architecture by ‘Uncle Bob’.

Eh, I’d honestly just use PostgreSQL for all that, it even has very advanced searching abilities that can out do elasticsearch in many cases, all while using the same database so no worry about things getting out of sync. Plus a chat app is mostly write and read with little to no ‘updating’, which is the perfect use-case for PostgreSQL (it flies the less ‘updating’ you do, mostly just reading and writing).

Any example for advances searchings with postgre? I’m interested :o

One example: Postgres full-text search is Good Enough!

Sure, it’s just that master-master story in postgres is still far from perfect, although postgres can make it far without any need to scale/replicate, but then (in case the chat app is international) I would want to spin up a database server on each continent in an attempt to reduce latency, and that would make postgres a bit harder to operate.

Also @rtj, you might want to read this A Comparison of Advanced, Modern Cloud Databases — brandur.org.

PostgreSQL has some pretty great libraries now for such replication, two main styles too (one replicates the raw data, always perfect consistency, the other replicates commands, much less bandwidth).

I feel this is a rare problem to have and once you do have it, you’ll have the resources to address it.

I feel like everyone here has forgotten that Whatsapp uses only Mnesia (or at least used too, I’m not sure about anything after 2014).