Batch statements

Session objects can be used to construct a logged batch statement and later execute it.

Background

Given

a running cassandra cluster with schema:

CREATE KEYSPACE simplex WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};
USE simplex;
CREATE TABLE songs (
  id uuid PRIMARY KEY,
  title text,
  album text,
  artist text,
  tags set<text>,
  data blob
);
CREATE TABLE cas_batch (k text, v int, PRIMARY KEY (k, v));

A batch of simple statements is executed

Given

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")

rows = session.execute("SELECT * FROM songs")

puts "songs contain #{rows.size} rows"

batch   = session.batch do |b|
            b.add("INSERT INTO songs (id, title, album, artist, tags)
                   VALUES (
                      756716f7-2e54-4715-9f00-91dcbea6cf50,
                      'La Petite Tonkinoise',
                      'Bye Bye Blackbird',
                      'Joséphine Baker',
                      {'jazz', '2013'}
                   )")
            b.add("INSERT INTO songs (id, title, album, artist, tags)
                   VALUES (
                      f6071e72-48ec-4fcb-bf3e-379c8a696488,
                      'Die Mösch',
                      'In Gold',
                      'Willi Ostermann',
                      {'kölsch', '1996', 'birds'}
                   )")
            b.add("INSERT INTO songs (id, title, album, artist, tags)
                   VALUES (
                      fbdf82ed-0063-4796-9c7c-a3d4f47b4b25,
                      'Memo From Turner',
                      'Performance',
                      'Mick Jager',
                      {'soundtrack', '1991'}
                   )")
          end

puts "inserting rows in a batch"

session.execute(batch, consistency: :all)
rows = session.execute("SELECT * FROM songs")

puts "songs contain #{rows.size} rows"

When

it is executed

Then

its output should contain:

songs contain 0 rows
inserting rows in a batch
songs contain 3 rows

A batch of simple statements with parameters is executed

Given

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")

rows = session.execute("SELECT * FROM songs")

puts "songs contain #{rows.size} rows"

batch   = session.batch do |b|
            b.add("INSERT INTO songs (id, title, album, artist, tags) VALUES (?, ?, ?, ?, ?)",
                  [Cassandra::Uuid.new('756716f7-2e54-4715-9f00-91dcbea6cf50'),
                  'La Petite Tonkinoise',
                  'Bye Bye Blackbird',
                  'Joséphine Baker',
                  Set['jazz', '2013']]
            )
            b.add("INSERT INTO songs (id, title, album, artist, tags) VALUES (?, ?, ?, ?, ?)",
                  [Cassandra::Uuid.new('f6071e72-48ec-4fcb-bf3e-379c8a696488'),
                  'Die Mösch',
                  'In Gold',
                  'Willi Ostermann',
                  Set['kölsch', '1996', 'birds']]
            )
            b.add("INSERT INTO songs (id, title, album, artist, tags) VALUES (?, ?, ?, ?, ?)",
                  [Cassandra::Uuid.new('fbdf82ed-0063-4796-9c7c-a3d4f47b4b25'),
                  'Memo From Turner',
                  'Performance',
                  'Mick Jager',
                  Set['soundtrack', '1991']]
            )
          end

puts "inserting rows in a batch"

session.execute(batch, consistency: :all)
rows = session.execute("SELECT * FROM songs")

puts "songs contain #{rows.size} rows"

When

it is executed

Then

its output should contain:

songs contain 0 rows
inserting rows in a batch
songs contain 3 rows

A prepared statement is executed in a batch

Given

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")

rows = session.execute("SELECT * FROM songs")

puts "songs contain #{rows.size} rows"

insert  = session.prepare("INSERT INTO songs (id, title, album, artist, tags) VALUES (?, ?, ?, ?, ?)")
batch   = session.batch do |b|
            b.add(insert,
                  [Cassandra::Uuid.new('756716f7-2e54-4715-9f00-91dcbea6cf50'),
                  'La Petite Tonkinoise',
                  'Bye Bye Blackbird',
                  'Joséphine Baker',
                  Set['jazz', '2013']]
            )
            b.add(insert,
                  [Cassandra::Uuid.new('f6071e72-48ec-4fcb-bf3e-379c8a696488'),
                  'Die Mösch',
                  'In Gold',
                  'Willi Ostermann',
                  Set['kölsch', '1996', 'birds']]
            )
            b.add(insert,
                  [Cassandra::Uuid.new('fbdf82ed-0063-4796-9c7c-a3d4f47b4b25'),
                  'Memo From Turner',
                  'Performance',
                  'Mick Jager',
                  Set['soundtrack', '1991']]
            )
          end

puts "inserting rows in a batch"

session.execute(batch, consistency: :all)
rows = session.execute("SELECT * FROM songs")

puts "songs contain #{rows.size} rows"

When

it is executed

Then

its output should contain:

songs contain 0 rows
inserting rows in a batch
songs contain 3 rows

A cas batch is never applied more than once

Given

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")

statement = session.prepare("INSERT INTO cas_batch (k, v) VALUES (?, ?) IF NOT EXISTS")
batch = session.batch

batch.add("INSERT INTO cas_batch (k, v) VALUES ('key1', 0)")
batch.add(statement, ["key1", 1])
batch.add(statement, ["key1", 2])

results =  session.execute(batch)
rows = results.first
puts "batch applied? #{rows["[applied]"]}"

results =  session.execute(batch)
rows = results.first
puts "batch applied? #{rows["[applied]"]}"

When

it is executed

Then

its output should contain:

batch applied? true
batch applied? false

Cassandra 1.2 doesn’t support batch statements

Given

the following example:

require 'cassandra'

cluster = Cassandra.cluster
session = cluster.connect("simplex")
batch   = session.batch

batch.add("INSERT INTO cas_batch (k, v) VALUES ('key1', 0)")

begin
  session.execute(batch)
rescue => e
  puts "#{e.class.name}: #{e.message}"
end

When

it is executed

Then

its output should contain:

Cassandra::Errors::ClientError: Batch statements are not supported by the current version of Apache Cassandra