Crystal/Kemal JSON API Server

This is a JSON API server built with Kemal in Crystal. It is designed to be compared with an Actix-web server. While Actix-web is known for its safety and speed, Kemal offers faster development and easier maintenance.

Read more : https://studiozenkai.com/post/crystal-high-performance/

Getting Started

Prerequisites

Make sure you have Crystal installed on your machine. You can install it using Homebrew:

brew install crystal

Installation

Clone the repository and navigate into the project directory:

git clone git@github.com:heri/crystal_pure_api.git
cd crystal_pure_api

Install the required dependencies:

shards install
psql -U postgres
CREATE DATABASE profiling;
\c profiling
CREATE TABLE users (id SERIAL PRIMARY KEY, firstName VARCHAR(255));

Seed the table with the 10,000 rows the /db benchmark endpoint reads from:

bin/seed

Running the Application

Compile the application:

crystal build main.cr --release

Crystal runs single-threaded per process, so main.cr binds with reuse_port and bin/server starts one worker process per CPU core, letting the kernel load-balance connections across them:

KEMAL_PORT=3000 bin/server

Set WORKERS to override the worker count instead of using all cores.

Each worker keeps its own Postgres connection pool, sized by DB_POOL_SIZE (default 25) so connections are pre-warmed instead of opened and closed on demand under load.

The server should now be running and accessible at http://localhost:3000.

Endpoints

• GET /json: Returns a static JSON payload with no database access. Mirrors TechEmpower's JSON Serialization test.
• GET /db: Fetches one row out of the 10,000-row users table by a server-generated random id. Mirrors TechEmpower's Single Database Query test.
• GET /users: Returns a list of users in HTML format.
• POST /webhook: Updates a user's first name. Expects a JSON payload with firstName and Id.

Contributing

Feel free to submit issues and pull requests.

License

This project is licensed under the MIT License.