ScalarDB Server Sample

This is a sample application that uses ScalarDB Server, a gRPC server that implements ScalarDB interface, as a backend. For using the native ScalarDB library, please refer to Getting Started. More information about ScalarDB Server can be found here.

Sample application

The sample application is a simple electronic money application that has the following features:

• Charge an amount to a user_id
• Pay an amount from a user_id to another user_id
• Get a balace of a user_id

Prerequisites

• Java (OpenJDK 8 or higher)
• Gradle
• Docker, Docker Compose

Set up

ScalarDB Server

In this sample, we will use Cassandra as storage for ScalarDB Server. The configuration of ScalarDB Server is shown below. (It is also stored in database.properties)

# Comma separated contact points
scalar.db.contact_points=cassandra

# Port number for all the contact points. Default port number for each database is used if empty.
scalar.db.contact_port=9042

# Credential information to access the database
scalar.db.username=cassandra
scalar.db.password=cassandra

# Storage implementation
scalar.db.storage=cassandra

Clone the ScalarDB samples repository

Open Terminal, then clone the ScalarDB samples repository by running the following command:

$ git clone https://github.com/scalar-labs/scalardb-samples

Then, go to the directory with this sample by running the following command:

$ cd scalardb-samples/scalardb-server-sample

Start Cassandra

To start Cassandra and ScalarDB Server, we use the following command. Please note that we should wait around a bit more than one minute because ScalarDB container has to wait for Cassandra container to be fully started.

$ docker-compose -f docker-compose-cassandra.yml up -d

For using other databases as the backend for ScalarDB Server, we can change the configuration of database.properties according to Getting Started. After that we can start ScalarDB Server using docker-compose.yml instead.

ScalarDB client

The sample application uses a client that implements ScalarDB interface. Thus, you can configure the client in the same way as the server-side. But, in this case, you need to specify the server as a contact point and grpc for the storage and transaction_manager configuration as follows. (it is stored in scalardb-client.properties).

# Comma separated contact points
scalar.db.contact_points=localhost

# Port number for all the contact points. Default port number for each database is used if empty.
scalar.db.contact_port=60051

# Storage implementation
scalar.db.storage=grpc

# The type of the transaction manager
scalar.db.transaction_manager=grpc

Set up database schema

Now you apply the database schema of the sample application as shown below. (It is stored in emoney.json).

{
  "emoney.account": {
    "transaction": true,
    "partition-key": [
      "id"
    ],
    "clustering-key": [],
    "columns": {
      "id": "TEXT",
      "balance": "INT"
    }
  }
}

You then apply the schema with the following command. Please download the schema tool scalardb-schema-loader-<version>.jar that can be found in releases of ScalarDB.

$ java -jar scalardb-schema-loader-<version>.jar --config scalardb-client.properties --schema-file emoney.json --coordinator

Note that --coordinator is specified to create the coordinator table needed for transactions.

Run the sample

• Charge 1000 to user1:

$ ./gradlew run --args="-action charge -amount 1000 -to user1"

• Charge 0 to merchant1 (Just create an account for merchant1):

$ ./gradlew run --args="-action charge -amount 0 -to merchant1"

• Pay 100 from user1 to merchant1:

$ ./gradlew run --args="-action pay -amount 100 -from user1 -to merchant1"

• Get the balance of user1:

$ ./gradlew run --args="-action getBalance -id user1"

• Get the balance of merchant1:

$ ./gradlew run --args="-action getBalance -id merchant1"

Storage abstraction

ScalarDB Server also supports Storage API. The following describes a sample of Storage API.

Set up database schema

If you have created the tables for transactions, you can delete them with the -D option as follows.

$ java -jar scalardb-schema-loader-<version>.jar --config scalardb-client.properties --schema-file emoney.json --coordinator -D

You can create a schema by setting transaction to false. (The updated schema is stored in emoney-storage.json)

{
  "emoney.account": {
    "transaction": false,
    "partition-key": [
      "id"
    ],
    "clustering-key": [],
    "columns": {
      "id": "TEXT",
      "balance": "INT"
    }
  }
}

You then apply the schema with the following command.

$ java -jar scalardb-schema-loader-<version>.jar --config scalardb-client.properties --schema-file emoney-storage.json

Run the sample with Storage API

• Charge 1000 to user1:

$ ./gradlew -Pstorage run --args="-action charge -amount 1000 -to user1"

• Charge 0 to merchant1 (Just create an account for merchant1):

$ ./gradlew -Pstorage run --args="-action charge -amount 0 -to merchant1"

• Pay 100 from user1 to merchant1:

$ ./gradlew -Pstorage run --args="-action pay -amount 100 -from user1 -to merchant1"

• Get the balance of user1:

$ ./gradlew -Pstorage run --args="-action getBalance -id user1"

• Get the balance of merchant1:

$ ./gradlew -Pstorage run --args="-action getBalance -id merchant1"

Clean up

To stop Cassandra and ScalarDB Server, run the following command:

$ docker-compose -f docker-compose-cassandra.yml down