jasonmartens / cassandra-streaming

Sample project to stream data from Cassandra to a browser via websockets

Streaming Cassandra to a Browser

This is an experimental project to try out streaming from Cassandra to a browser.

The cassandra code was taken from the Phantom examples: https://github.com/outworkers/phantom/tree/develop/phantom-example/src

The Scala-JS examples were taken from this example: https://github.com/jrudolph/akka-http-scala-js-websocket-chat

The goal is to stream data from a DB query to the browser, with some kind of manual backpressure. This allows retrieving data from the database without the hassle of paging the results.

To allow the developer control over the number of records returned, a "manual" backpressure mechanism is used. The developer can signal the number of records desired, which is the demand. To implement this, a custom akka-streams graph stage is used with 2 inputs and one output. The inputs are the data stream, and a stream of demand messages, and the output is the requested number of data elements.

Assumptions

You have a cassandra database at the IP(s) and port listed in the application.conf

Sample Data

The list of names comes from the US Census Bureau. To insert the sample data, run the InsertSampleData app:

sbt
project backend
runMain com.jasonmartens.cassandra.InsertSampleData

Running the app

Either run the Boot app from your IDE, or from sbt:

sbt
project backend
re-start