The simple, lightweight, distributed in-memory key-value store using netty.
Focusing on supporiting scalable, high-availability application.

---

Introduction

Keycafe is the simple distributed key-value in-memory database implementation supporting String data structure, for research purpose how to build the simple distributed system from scratch. Keycafe is focusing on stroing key-value entry in memory which means reading faster than existing relational database. Also, more than one nodes form a cluster system and distribute key-value entries to extend the entire throughput. User can do GET, SET, DELETE commands. Entries are stored in slot, the logical block of Keycafe, which came from the keys distribution model of Redis. There are multiple logical slots in Keycafe cluster and the hash alogorithm is used to map the key to consistent hash slot. Slots are maintained by Keycafe cluster nodes.

Clustering

Slots

Architecture

Coordinate Server

coordinate-server is a centralized service for maintaining server configuration or providing a solution to divide slots which is shared resource of cluster into Keycafe server cluster. With the server configuration information provided by coordinate-server, Keycafe server can discover other Keycafe servers and have a chance to share slots fairly between nodes.

Keycafe Server

As explain above, keycafe-server stores key-value entries and read value faster than existing relational database. User can read, write, and delete values with the commands of get, set, and delete. Forming a cluster, keycafe-server nodes share logical slots between their cluster nodes.

Keycafe Client

Because Keycafe uses its own TCP binary protocol, keycafe-client provides a simple method to communicate Keycafe server.

• Example code

public class Main() {
    public static void main(String[] args) {
        KeycafeCluster keycafe = new KeycafeCluster("localhost", 9814);
        System.out.println(keycafe.set("example_key", "KEY"));  // "ok"
        System.out.println(keycafe.get("example_key"));         // "KEY"
        System.out.println(keycafe.get("no_key"));              // null
        keycafe.close();
    }
}

Example (auth-server, auth-web)

auth-server is a simple authentication server to show how to use Keycafe key-value store. Displaying a simple auth with auth-web, the example provides the web-based use case in an application level.

Build and run

$ sh build.sh
$ sh run-coordinate.sh
$ sh run-server.sh config.yaml
$ sh run-example-server.sh
$ sh run-example-web.sh
# and try with email: 'limpett0@smugmug.com', password: 'pCHecmGBZ7'
# for detail information, see: examples/auth-server/src/main/resources/data.sql

Gradle

• Build

$ ./gradlew build

• Make Executable jar

$ ./gradlew :coordinate-server:jar
$ ./gradlew :server:jar

• run

$ java -jar coordinate-server/build/libs/coordinate-server-0.0.1.jar
$ java -jar server/build/libs/server-0.0.1.jar config.yaml

Docker

• Dockerfile

$ docker build -f docker/coordinate-server/Dockerfile .
$ docker build -f docker/server/Dockerfile .

• docker-compose build

$  docker-compose -f docker/docker-compose.yml build

Internal specification

Keycafe commands

• Request
• Reply

Keycafe cluster

• TCP connection bus
• Keycafe cluster messages
• Client keycafe cluster discover

Coordination

• Register node information.
• Notify new node joining the cluster.