Nguyễn Khánk's Wiki

# Apache Cassandra

  • Developed by Facebook in 2007. Gifted to Apache 2/2010
  • NoSQL but has structure
  • A database - column family
  • Can use SQL to manipulate with data
  • Peer to peer database, sharding, more nodes more performance

# Column-oriented Database

Its architecture uses (a) persistent, sparse matrix, multi-dimensional mapping (row-value, column-value, and timestamp) in a tabular format meant for massive scalability (over and above the petabyte scale).

Column-oriented

Source:

  • https://stackoverflow.com/questions/62010368/what-exactly-is-a-wide-column-store
  • https://www.baeldung.com/cassandra-column-family-data-model

# Ring cluster

cluster

  • Each nodes will be assigned a range of token.
  • Client could connect any nodes to write, that node will become coordinator node.
  • Partition keys will be hashed into a token. Coordinator will base on the token to know which node we can store the data.
  • When a Cassandra node becomes unavailable, processing continues and failed writes are temporarily saved as hints on the coordinator. If the hints have not expired, they are applied to the node when it becomes available.

# Replication Factor

  • Replication Factor (RF) = number copies we want to store
  • Replication node will be defined by Replication Strategy
  • Simple strategy = next 2 nodes

# Consistent hashing

... TODO

# Data consistency

WRITE READ Consistent Read Availability Write Availability
All All ✅ Low Low
Quorum All ✅ Low Medium
✅  One All ✅ Low High
All Quorum ✅ Medium Low
✅ Quorum Quorum ✅ Medium Medium
One Quorum ❌ Medium High
✅ All One ✅ High Low
Quorum One ❌ High Medium
One One ❌ High High

# Keys

  • Each table requires a unique primary key.
  • The first field listed is the partition key, since its hashed value is used to determine the node to store the data.
  • If those fields are wrapped in parentheses then the partition key is composite. Otherwise the first field is the partition key.
  • Any fields listed after the partition key are called clustering columns. These store data in ascending or descending order within the partition for the fast retrieval of similar values.
  • All the fields together are the primary key.

All data has the same partison key will be store at the same node

We should only access data using the partison key

Every node has 256 virtual nodes in default

# CQL

Tables should reflect the queries we are trying to make

# Keyspace

# Table

# Selection

Write time

SELECT car_make, car_model, writetime(car_model)
FROM employee_by_car_make;

Allow filtering

SELECT * FROM employee_by_id
WHERE name = 'John' ALLOW FILTERING;

# Update

Time to live (60seconds), value will be null after the given time.

Use case: token / coupon is only valid in 24hours

UPDATE employee_by_car_make 
USING TTL 60 
SET car_model='TRUCK'
WHERE car_make'BMW' AND id='2';

# Collections

UPDATE employee_by_id
SET phone = {'123', '321'}
WHERE id = 1

Append

UPDATE employee_by_id
SET phone = phone + {'555', '444'}
WHERE id = 1

Remove

UPDATE employee_by_id
SET phone = phone - {'555'}
WHERE id = 1

# UUID

# Refs

← Elastic Search →