Apache Cassandra

Core Concepts

Cassandra's data model is based on a wide-column store design:

Example table structure:

-- Create keyspace with replication
CREATE KEYSPACE my_app WITH replication = {
    'class': 'NetworkTopologyStrategy',
    'datacenter1': 3
};

-- Create table with composite primary key
CREATE TABLE my_app.user_events (
    user_id UUID,
    event_time TIMESTAMP,
    event_type TEXT,
    event_data MAP<TEXT, TEXT>,
    PRIMARY KEY ((user_id), event_time)
) WITH CLUSTERING ORDER BY (event_time DESC);

Common CQL Operations

-- Insert data
INSERT INTO user_events (user_id, event_time, event_type, event_data)
VALUES (uuid(), toTimestamp(now()), 'login', {'ip': '192.168.1.1'});

-- Query by partition key (efficient)
SELECT * FROM user_events
WHERE user_id = 123e4567-e89b-12d3-a456-426614174000
AND event_time > '2024-01-01';

-- Update with TTL (auto-expire after 30 days)
UPDATE user_events USING TTL 2592000
SET event_data = {'status': 'processed'}
WHERE user_id = 123e4567-e89b-12d3-a456-426614174000
AND event_time = '2024-01-15 10:30:00';

-- Batch operations (atomic within partition)
BEGIN BATCH
    INSERT INTO user_events ...
    INSERT INTO user_events ...
APPLY BATCH;

Python Driver Example

# Install: pip install cassandra-driver

from cassandra.cluster import Cluster
from cassandra.auth import PlainTextAuthProvider
from cassandra.query import SimpleStatement, ConsistencyLevel
import uuid

# Connect to cluster
auth_provider = PlainTextAuthProvider('username', 'password')
cluster = Cluster(['node1.example.com', 'node2.example.com'],
                  auth_provider=auth_provider)
session = cluster.connect('my_keyspace')

# Insert data
insert_stmt = session.prepare("""
    INSERT INTO user_events (user_id, event_time, event_type, event_data)
    VALUES (?, toTimestamp(now()), ?, ?)
""")
session.execute(insert_stmt, [uuid.uuid4(), 'page_view', {'page': '/home'}])

# Query with consistency level
query = SimpleStatement(
    "SELECT * FROM user_events WHERE user_id = %s",
    consistency_level=ConsistencyLevel.LOCAL_QUORUM
)
results = session.execute(query, [user_id])
for row in results:
    print(f"{row.event_time}: {row.event_type}")