Automatic reconnection

Ruby driver automatically reestablishes failed connections to Cassandra cluster. It will use a reconnection policy to determine retry intervals.

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

And

a file named “printing_listener.rb” with:

class PrintingListener
  def initialize(io)
    @out = io
  end

  def host_found(host)
    @out.puts("Host #{host.ip} is found")
    @out.flush
  end

  def host_lost(host)
    @out.puts("Host #{host.ip} is lost")
    @out.flush
  end

  def host_up(host)
    @out.puts("Host #{host.ip} is up")
    @out.flush
  end

  def host_down(host)
    @out.puts("Host #{host.ip} is down")
    @out.flush
  end
end

And

the following example:

require 'cassandra'
require 'printing_listener'

interval = 2 # reconnect every 2 seconds
policy   = Cassandra::Reconnection::Policies::Constant.new(interval)
cluster  = Cassandra.cluster(
             listeners: [PrintingListener.new($stdout)],
             reconnection_policy: policy,
             consistency: :one
           )
session = cluster.connect

$stdout.puts("=== START ===")
$stdout.flush
until (input = $stdin.gets).nil? # block until closed
  query = input.chomp
  begin
    execution_info = session.execute(query).execution_info
    $stdout.puts("Query #{query.inspect} fulfilled by #{execution_info.hosts.last.ip}")
  rescue => e
    $stdout.puts("Query #{query.inspect} failed with #{e.class.name}: #{e.message}")
  end
  $stdout.flush
end
$stdout.puts("=== STOP ===")
$stdout.flush

And

it is running interactively

And

I wait for its output to contain “START”

Driver reconnects when all hosts are down

When

node 1 stops

When

node 2 stops

When

node 3 stops

And

I type “SELECT * FROM simplex.songs”

And

node 1 starts

And

I wait for 3 seconds

And

I type “SELECT * FROM simplex.songs”

And

I close the stdin stream

Then

its output should contain:

Query "SELECT * FROM simplex.songs" failed with Cassandra::Errors::NoHostsAvailable: All hosts down

And

its output should contain:

Query "SELECT * FROM simplex.songs" fulfilled by 127.0.0.1

Automatic reconnection

Background

Driver reconnects when all hosts are down

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