Building a Cassandra based application
from scratch Patrick McFadin Cassandra Summit 2012 #cassandra12

This is me• Chief Architect
at Hobsons – Hobsons is an education services company. More here: www.hobsons.com• Cassandra user since .7• Follow me here: @PatrickMcFadin

Goals• Take a new concept•
What’s the data model?!?!• Some sample code• You get homework! (If you want)

Here’s the plan• Conceptualize a
new application• Identify the entity tables• Identify query tables• Code. Rinse. Repeat.• Deploy• …• Profit! * I’ll be using the term Tables which is equivalent to Column Families

www.killrvideos.com Video Tit le User
name Recommended D ipt ion escrStart with a Meow Ads concept by Google Video Sharing Website Rat ing: Tags: Foo Bar Upload New! Comment s*Cat drawing by goodrob13 on Flickr

Break down the features• Post
a video*• View a video• Add a comment• Rate a video• Tag a video * Not talking about transcoding! Check out zencoder.com, it’s pretty sweet.

Create Entity Tables Basic storage
unit

Users password FirstName LastName Username•
Similar to a RDBMS table. Fairly fixed columns• Username is unique• Use secondary indexes on firstname and lastname for lookup• Adding columns with Cassandra is super easy CREATE TABLE users ( username varchar PRIMARY KEY, firstname varchar, lastname varchar, password varchar );

Users: The set codestatic void
setUser(User user, Keyspace keyspace) { // Create a mutator that allows you to talk to casssandra Mutator<String> mutator = HFactory.createMutator(keyspace, stringSerializer); try { // Use the mutator to insert data into our table mutator.addInsertion(user.getUsername(), "users", HFactory.createStringColumn("firstname", user.getFirstname())); mutator.addInsertion(user.getUsername(), "users”, HFactory.createStringColumn("lastname", user.getLastname())); mutator.addInsertion(user.getUsername(), "users", HFactory.createStringColumn("password", user.getPassword())); // Once the mutator is ready, execute on cassandra mutator.execute(); } catch (HectorException he) { he.printStackTrace(); }} You can implement the get…

Videos UserName Description Tags VideoId
VideoName <UUID>• Use a UUID as a row key for uniqueness• Allows for same video names• Tags should be stored in some sort of delimited format• Index on username may not be the best plan CREATE TABLE videos ( videoid uuid PRIMARY KEY, videoname varchar, username varchar, description varchar, tags varchar );

Videos: The get codestatic Video
getVideoByUUID(UUID videoId, Keyspace keyspace){ Video video = new Video(); //Create a slice query. Well be getting specific column names SliceQuery<UUID, String, String> sliceQuery = HFactory.createSliceQuery(keyspace, uuidSerializer, stringSerializer, stringSerializer); sliceQuery.setColumnFamily("videos"); sliceQuery.setKey(videoId); sliceQuery.setColumnNames("videoname","username","description","tags"); // Execute the query and get the list of columns ColumnSlice<String,String> result = sliceQuery.execute().get(); // Get each column by name and add them to our video object video.setVideoName(result.getColumnByName("videoname").getValue()); video.setUsername(result.getColumnByName("username").getValue()); video.setDescription(result.getColumnByName("description").getValue()); video.setTags(result.getColumnByName("tags").getValue().split(",")); return video;} You can implement the set…

Comments VideoId Username:<timestamp> .. Username:<timestamp>
<UUID> Time Order• Videos have many comments• Use Composite Columns to store user and time• Value of each column is the text of the comment• Order is as inserted• Use getSlice() to pull some or all of the comments CREATE TABLE comments ( videoid uuid PRIMARY KEY comment varchar );

Rating a video rating_count rating_total
VideoId <UUID> <counter> <counter>• Use counter for single call update• rating_count is how many ratings were given• rating_total is the sum of rating• Ex: rating_count = 5, rating_total = 23, avg rating = 23/5 = 4.6 CREATE TABLE video_rating ( videoid uuid PRIMARY KEY, rating_counter counter, rating_total counter);* * Only valid in CQL 3+

Video Event start_<timestamp> stop_<timestamp> start_<timestamp>
VideoId:Username video_<timestamp> Time Order• Track viewing events• Combine Video ID and Username for a unique row• Stop time can be used to pick up where they left off• Great for usage analytics later CREATE TABLE video_event ( videoid_username varchar PRIMARY KEY, event varchar );

Create Query TablesIndexes to support
fast lookups

Lookup Video By Username VideoId:<timestamp>
.. VideoId:<timestamp> Username• Username is unique• One column for each new video uploaded• Column slice for time span. From x to y• VideoId is added the same time a Video record is added CREATE TABLE username_video_index ( username varchar PRIMARY KEY, videoid_timestamp varchar );

Videos by Tag VideoId ..
VideoId tag• Tag is unique regardless of video• Great for “List videos with X tag”• Tags have to be updated in Video and Tag at the same time• Index integrity is maintained in app logic CREATE TABLE tag_index ( tag varchar PRIMARY KEY, videoid varchar );

Deployment strategies• Measure your risk
– Replication factor? – Multi-datacenter? – Cost?• Performance – Today != tomorrow. Scale when needed – Have a expansion plan ready

Wrap up• Similar data model
process to RDBMS… to start• Query -> Index table• Don’t be afraid to write in multiple tables at once• Bonus points: Hadoop and Solr!

Go play!• Go to: http://github.com/pmcfadin•
Look for projects with cassandra12• Clone or fork my examples• Implement stubbed methods• Send me your solutions: pmcfadin@gmail.com• Follow me for updates: @PatrickMcFadin

Thank You!Connect with me at
@PatrickMcFadin Or linkedIn Conference tag #cassandra12