More Cassandra

There's a lot written about the Cassandra data model, here's a good one: http://javamaster.wordpress.com/2010/03/22/apache-cassandra-quick-tour/

Let's set up a small system to work together with one little web app I did some years ago (at that time with MySql). Prepare a glossary for the Distributed Software Architecture Course for the fall. The data model should support two operations:

* List all terms/explanations in alphabetic order (over the term of course)
* List all terms/explanations in alphabetic order in a given interval

Shouldn't be too difficult, once you forget about ACID. Actually, in this case, with the small amount of "use cases", it seems I can just copy the basic SQL idea, equating a table with a column family. How did the SQL look like?

CREATE DATABASE IF NOT EXISTS DSAGlossary;
USE DSAGlossary;
DROP TABLE IF EXISTS Reference;

CREATE TABLE DSAGlossary.Reference (
 refID INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
 term VARCHAR(50) NOT NULL,
 description VARCHAR(250) NOT NULL,
 PRIMARY KEY (refID)
)

That doesn't look too difficult - the problems may arise with more cases. Here it's more or less the same structure - apart from the missing artificial primary key.

create keyspace DSAGlossary;
use DSAGlossary;

create column family Reference with
  comparator = UTF8Type and
  column_metadata =
  [
      {column_name: term, validation_class: UTF8Type,
                          index_type: KEYS},
      {column_name: expl, validation_class: UTF8Type}
  ];

We need this KEYS in order to have access to a column over the term. Feed this into the Cassandra implementation - in the Cassandra home directory:

1. Start it with bin/cassandra start&
2. Use the CLI to feed the script in:

bin/cassandra-cli -host localhost -port 9160 -f glossary.txt
Connected to: "Test Cluster" on localhost/9160
1361c18a-7b18-11e0-b561-e700f669bcfc
Waiting for schema agreement...
... schemas agree across the cluster
Authenticated to keyspace: DSAGlossary
13eb63eb-7b18-11e0-b561-e700f669bcfc
Waiting for schema agreement...
... schemas agree across the cluster

Sounds like a success (you're never completely sure); so add one entry:

bin/cassandra-cli -host localhost -port 9160
Connected to: "Test Cluster" on localhost/9160
Welcome to cassandra CLI.

Type 'help;' or '?' for help. Type 'quit;' or 'exit;' to quit.
[default@unknown] use DSAGlossary;
Authenticated to keyspace: DSAGlossary
[default@DSAGlossary] set Reference['Cassandra']['term']
                     = 'Cassandra';
Value inserted.
[default@DSAGlossary] set Reference['Cassandra']['expl']
                     = 'http://en.wikipedia.org/wiki/Apache_Cassandra';
Value inserted.

Still fine! Get it back, maybe?

[default@DSAGlossary] get Reference where term
                     = 'Cassandra';
-------------------
RowKey: Cassandra
=> (column=expl, value=http://en.wikipedia.org/wiki/Apache_Cassandra,  
     timestamp=1305041351336000)
=> (column=term, value=Cassandra,
     timestamp=1305041338862000)

1 Row Returned.

Ok! Next time: Get access from Java (or any other language).