class Deimos::Utils::DbPoller

Class which continually polls the database and sends Kafka messages.

Constants

BATCH_SIZE

Attributes

id[R]

Needed for Executor so it can identify the worker

Public Class Methods

new(config) click to toggle source

@param config [Deimos::Configuration::ConfigStruct]

# File lib/deimos/utils/db_poller.rb, line 33
def initialize(config)
  @config = config
  @id = SecureRandom.hex
  begin
    @producer = @config.producer_class.constantize
  rescue NameError
    raise "Class #{@config.producer_class} not found!"
  end
  unless @producer < Deimos::ActiveRecordProducer
    raise "Class #{@producer.class.name} is not an ActiveRecordProducer!"
  end
end
start!() click to toggle source

Begin the DB Poller process.

# File lib/deimos/utils/db_poller.rb, line 17
def self.start!
  if Deimos.config.db_poller_objects.empty?
    raise('No pollers configured!')
  end

  pollers = Deimos.config.db_poller_objects.map do |poller_config|
    self.new(poller_config)
  end
  executor = Sigurd::Executor.new(pollers,
                                  sleep_seconds: 5,
                                  logger: Deimos.config.logger)
  signal_handler = Sigurd::SignalHandler.new(executor)
  signal_handler.run!
end

Public Instance Methods

fetch_results(time_from, time_to) click to toggle source

@param time_from [ActiveSupport::TimeWithZone] @param time_to [ActiveSupport::TimeWithZone] @return [ActiveRecord::Relation]

# File lib/deimos/utils/db_poller.rb, line 126
def fetch_results(time_from, time_to)
  id = @producer.config[:record_class].primary_key
  quoted_timestamp = ActiveRecord::Base.connection.quote_column_name(@config.timestamp_column)
  quoted_id = ActiveRecord::Base.connection.quote_column_name(id)
  @producer.poll_query(time_from: time_from,
                       time_to: time_to,
                       column_name: @config.timestamp_column,
                       min_id: @info.last_sent_id).
    limit(BATCH_SIZE).
    order("#{quoted_timestamp}, #{quoted_id}")
end
last_updated(record) click to toggle source

@param record [ActiveRecord::Base] @return [ActiveSupport::TimeWithZone]

# File lib/deimos/utils/db_poller.rb, line 94
def last_updated(record)
  record.public_send(@config.timestamp_column)
end
process_batch(batch) click to toggle source

@param batch [Array<ActiveRecord::Base>]

# File lib/deimos/utils/db_poller.rb, line 139
def process_batch(batch)
  record = batch.last
  id_method = record.class.primary_key
  last_id = record.public_send(id_method)
  last_updated_at = last_updated(record)
  @producer.send_events(batch)
  @info.attributes = { last_sent: last_updated_at, last_sent_id: last_id }
  @info.save!
end
process_updates() click to toggle source

Send messages for updated data.

# File lib/deimos/utils/db_poller.rb, line 99
def process_updates
  return unless should_run?

  time_from = @config.full_table ? Time.new(0) : @info.last_sent.in_time_zone
  time_to = Time.zone.now - @config.delay_time
  Deimos.config.logger.info("Polling #{@producer.topic} from #{time_from} to #{time_to}")
  message_count = 0
  batch_count = 0

  # poll_query gets all the relevant data from the database, as defined
  # by the producer itself.
  loop do
    Deimos.config.logger.debug("Polling #{@producer.topic}, batch #{batch_count + 1}")
    batch = fetch_results(time_from, time_to).to_a
    break if batch.empty?

    batch_count += 1
    process_batch(batch)
    message_count += batch.size
    time_from = last_updated(batch.last)
  end
  Deimos.config.logger.info("Poll #{@producer.topic} complete at #{time_to} (#{message_count} messages, #{batch_count} batches}")
end
retrieve_poll_info() click to toggle source

Grab the PollInfo or create if it doesn't exist.

# File lib/deimos/utils/db_poller.rb, line 70
def retrieve_poll_info
  ActiveRecord::Base.connection.reconnect! unless ActiveRecord::Base.connection.open_transactions.positive?
  new_time = @config.start_from_beginning ? Time.new(0) : Time.zone.now
  @info = Deimos::PollInfo.find_by_producer(@config.producer_class) ||
          Deimos::PollInfo.create!(producer: @config.producer_class,
                                   last_sent: new_time,
                                   last_sent_id: 0)
end
should_run?() click to toggle source

Indicate whether this current loop should process updates. Most loops will busy-wait (sleeping 0.1 seconds) until it's ready. @return [Boolean]

# File lib/deimos/utils/db_poller.rb, line 88
def should_run?
  Time.zone.now - @info.last_sent - @config.delay_time >= @config.run_every
end
start() click to toggle source

Start the poll: 1) Grab the current PollInfo from the database indicating the last time we ran 2) On a loop, process all the recent updates between the last time we ran and now.

# File lib/deimos/utils/db_poller.rb, line 51
def start
  # Don't send asynchronously
  if Deimos.config.producers.backend == :kafka_async
    Deimos.config.producers.backend = :kafka
  end
  Deimos.config.logger.info('Starting...')
  @signal_to_stop = false
  retrieve_poll_info
  loop do
    if @signal_to_stop
      Deimos.config.logger.info('Shutting down')
      break
    end
    process_updates
    sleep 0.1
  end
end
stop() click to toggle source

Stop the poll.

# File lib/deimos/utils/db_poller.rb, line 80
def stop
  Deimos.config.logger.info('Received signal to stop')
  @signal_to_stop = true
end