Recently I was exploring the use of PostgreSQL as a replacement for MongoDB. PostgreSQL has in recent versions great support for JSON. You can store JSON values and you can even make indices on JSON fields. When combined with node.js and its driver things look almost magical. You read from PostgreSQL and you get automatically a JavaScript object, JSON fields automatically embedded. But can we also use JSON for transporting results of queries themselves, especially joins? In MongoDB the idea is to embed such related documents. In PostgreSQL we could also embed them instead of joining them, but would that be faster? I made a benchmark to get answers.

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I am a big fan of the application architecture promoted by Meteor. I like declarative programming. You describe what you want and not how and the system does the rest. Reactive programming is very similar. You define how outputs should be computed from inputs, but when is this computed and how it is composed with other computations is left to the system. So you can define what is read from the database and send to the client. And how it is read on the client and transformed and send to the UI library. And then UI library can render this data. And every time something changes, the rest gets automatically recomputed, refreshed, re-rendered.

Meteor is tightly linked with MongoDB. They developed a complex piece of technology to provide reactive queries. Reactive queries are queries which after providing initial results they also continue providing any changes to those results as input data used in queries change. While I like MongoDB, I still prefer consistency tools provided by traditional SQL databases: transactions, foreign keys, joins and triggers. They are close to declarative programming as well. You define relations between data once and then the system makes sure data is consistent. I had to implement many of those features on top of MongoDB, like my package PeerDB.

This is why I made reactive-postgres node.js package. It provides exactly such reactive queries, but for PostgreSQL open source database. Its API is simple, on purpose, and because it should be. You provide a query, you get initial data, and then you get all changes. Try it out.