cassandra-ds220

Exercises for DataStax, DS220: Data Modeling Course

• Exercise 1
• Exercise 2
• Exercise 3

Exercise1

Open a terminal, and start Cassadra Query Language Shell(CQLSH) with command:

$ cqlsh

then execute cql statement in order to see all available keyspaces:

$ select * from system.schema_keyspaces;

the answer should be:

 keyspace_name | durable_writes | strategy_class                                  | strategy_options
---------------+----------------+-------------------------------------------------+----------------------------
    dse_system |           True | org.apache.cassandra.locator.EverywhereStrategy |                         {}
     OpsCenter |           True |     org.apache.cassandra.locator.SimpleStrategy | {"replication_factor":"1"}
        system |           True |      org.apache.cassandra.locator.LocalStrategy |                         {}
 system_traces |           True |     org.apache.cassandra.locator.SimpleStrategy | {"replication_factor":"2"}

Exercise2

Open a terminal, and start Cassadra Query Language Shell(CQLSH) with command:

$ cqlsh

then execute cql statement in order to create keyspace 'killrvideo' and to create table 'videos':

CREATE KEYSPACE IF NOT EXISTS killrvideo 
WITH REPLICATION = {
  'class' : 'SimpleStrategy',
  'replication_factor': 1
};

USE killrvideo;

CREATE TABLE IF NOT EXISTS videos (
    video_id TIMEUUID,
    added_date TIMESTAMP,
    description TEXT,
    title TEXT,
    user_id UUID,
    PRIMARY KEY(video_id)
);
 

then import data using COPY command from cqlsh

$ COPY videos(video_id, added_date, description, title, user_id) FROM '/root/labwork/exercise-2/videos.csv' WITH HEADER=true;

now you can check is data imported with

$ select count(*) from videos;

$ select * from videos;

at the end drop a keyspace 'killrvideo'

$ DROP KEYSPACE IF EXISTS killrvideo;

Exercise3

Open a terminal, and start Cassadra Query Language Shell(CQLSH) with command:

$ cqlsh

then execute cql statement in order to create table 'videos_by_title_year':

USE killrvideo;

CREATE TABLE IF NOT EXISTS videos_by_title_year (
    title TEXT,    
    added_year INT,
    added_date TIMESTAMP,
    description TEXT,
    user_id UUID,
    video_id UUID,
    PRIMARY KEY((title, added_year)) // for querying by title and added_year we need composite key
);
 

then import data using COPY command from cqlsh

$ COPY videos_by_title_year(title, added_year, added_date, description, user_id, video_id) FROM '/root/labwork/exercise-3/videos_by_title_year.csv' WITH HEADER=true;

now you can check is data imported with:

select count(*) from videos_by_title_year;

expected response is 430.

You can see all values in table with:

select * from videos_by_title_year;

Also you can find specific row in table with:

select * from videos_by_title_year where title = 'Another Phone Test' and added_year = 2015;

Note if you try to search without one of the columns which defines partition key

cqlsh:killrvideo> select * from videos_by_title_year where title = 'Another Phone Test';

it will return following error:

InvalidRequest: code=2200 [Invalid query] message="Partition key part added_year must be restricted since preceding part is"

The reason: hash function requires all partition key columns('...PRIMARY KEY((title, added_year))...'), otherwise it returns incorect hash -> in fact it is not possible to find node without all columns from partition key