Cassandra

Basics

• replication factor (RF)
• consistency level (CL) = QUORUM (Quorum referring to majority, 2 replicas in this case or RF/2 +1)
• coordinator
• SSTable
• memtable
• timestamps
• compaction: take small SSTables and merging them into bigger one

Intro

• keyspaces:
  • top-level namespace/container
  • similar to a relational database schema

  CREATE KEYSPACE killrvideo
  WITH REPLICATION = {
    'class': 'SimpleStrategy',
    'replication_factor': 1
  };
• USE switches between keyspaces

  USE killrvideo;
• Tables:
  • keyspaces contain tables
  • tables contain data

  CREATE TABLE table1 (
    column1 TEXT,
    column2 TEXT,
    column3 INT,
    PRIMARY KEY (column1)
  );
  
  CREATE TABLE users (
    user_id UUID,
    first_name TEXT,
    last_name TEXT,
    PRIMARY KEY (user_id)
  );
• Basic Data Types:
  • text: UTF8 encoded string, varchar is same as text, unbounded
  • int: Signed, 32 bits
  • timestamp: date and time, 64 bit integer, store number of seconds since Jan 1st 1970 GMT
• UUID && TIMEUUID
  • generate global unique id without communication between nodes
  • TIMEUUID embeds a TIMESTAMP value
• INSERT:

  INSERT INTO users (user_id, first_name, last_name)
  VALUES (uuid(), 'Joseph', 'Chu');
• SELECT:

  SELECT *
  FROM users;
  
  SELECT first_name, last_name
  FROM users;
  
  SELECT * 
  FROM users
  WHERE user_id = 4b516b3-ddf0-4c43-bab6-b91d674b64a5;
• COPY:
  • imports/exports CSV

  COPY table1 (column1, column2, column3) FROM 'table1data.csv';
  • header parameter skips the first line in the file

  COPY table1 (column1, column2, column3) FROM 'table1data.csv'
  WITH HEADER=true;
• get data into Cassandra:
  • COPY
  • Spark
  • Drivers
  • Etc.