Cassandra with the Python driver

Uses cassandra-driver 3.30. The code is an ordinary application for the original database; nothing in it knows about MachNoSQL.

The only change

cass-1.example.com,cass-2.example.com
machnosql-1.example.com,machnosql-2.example.com

The address comes from the environment variable CASSANDRA_CONTACT_POINTS, so switching to MachNoSQL changes configuration only.

Run

export CASSANDRA_CONTACT_POINTS='machnosql-1.example.com,machnosql-2.example.com'
pip install -r requirements.txt
python app.py

Credentials come from CASSANDRA_USERNAME and CASSANDRA_PASSWORD, the local data center from CASSANDRA_DC (default dc1).

Source

The program as it is kept and tested in the Mach Database NoSQL repository; highlighted lines read the connection setting.

app.py

"""Sensor readings on Cassandra, unchanged on MachNoSQL."""

import os
from datetime import datetime, timedelta, timezone

from cassandra.auth import PlainTextAuthProvider
from cassandra.cluster import Cluster
from cassandra.policies import DCAwareRoundRobinPolicy, TokenAwarePolicy

cluster = Cluster(
    contact_points=os.environ["CASSANDRA_CONTACT_POINTS"].split(","),
    port=9042,
    auth_provider=PlainTextAuthProvider(os.environ["CASSANDRA_USERNAME"], os.environ["CASSANDRA_PASSWORD"]),
    load_balancing_policy=TokenAwarePolicy(DCAwareRoundRobinPolicy(local_dc=os.environ.get("CASSANDRA_DC", "dc1"))),
    protocol_version=5,
)
session = cluster.connect()

session.execute(
    "CREATE KEYSPACE IF NOT EXISTS iot WITH replication = {'class': 'NetworkTopologyStrategy', 'dc1': 3}"
)
session.execute(
    "CREATE TABLE IF NOT EXISTS iot.readings (sensor text, at timestamp, value double, "
    "PRIMARY KEY (sensor, at)) WITH CLUSTERING ORDER BY (at DESC)"
)
session.execute("CREATE TABLE IF NOT EXISTS iot.sensors (sensor text PRIMARY KEY, owner text)")

insert = session.prepare("INSERT INTO iot.readings (sensor, at, value) VALUES (?, ?, ?) USING TTL 86400")
now = datetime.now(timezone.utc)
for minute in range(10):
    session.execute(insert, ("s-1", now - timedelta(minutes=minute), 20.0 + minute / 10))

rows = session.execute(
    "SELECT at, value FROM iot.readings WHERE sensor = %s AND at > %s LIMIT 5",
    ("s-1", now - timedelta(minutes=5)),
)
for row in rows:
    print(row.at, row.value)

applied = session.execute(
    "INSERT INTO iot.sensors (sensor, owner) VALUES (%s, %s) IF NOT EXISTS", ("s-1", "ada")
).was_applied
print("registered:", applied)

cluster.shutdown()

requirements.txt

cassandra-driver==3.30.1