Start at Time Delta

Overview

A time-delta subscription starts replay from a relative offset — "the last 60 seconds" — instead of a fixed timestamp or sequence number. It's the right tool when a consumer knows how long it was offline but not the exact moment it disconnected: a worker restarting after a deploy, a dashboard reconnecting after a blip, or a batch job that only cares about "recent" history. Computing an absolute cutoff yourself is bookkeeping the broker can do for you.

KubeMQ::PubSub::EventStoreStartPosition::START_AT_TIME_DELTA with start_position_value passes the offset to the broker, which resolves it to now - delta at subscription time, replays every stored event from that point forward, then hands off to live delivery — the same replay-to-live transition as an absolute-time or sequence-based start.

Gotchas: the delta is evaluated once, server-side, at subscription creation — it does not "slide" as time passes. A start_position_value of zero replays nothing and behaves like starting from new events only. And since the window is wall-clock based, clock skew between producers and the broker can shift which events land inside or outside the boundary.

Prerequisites

• KubeMQ server running on localhost:50000
• Ruby SDK installed (gem install kubemq)

Code

require 'kubemq'

address = ENV.fetch('KUBEMQ_ADDRESS', 'localhost:50000')
channel = 'ruby-events-store.start-at-time-delta'

begin
  client = KubeMQ::PubSubClient.new(address: address, client_id: 'es-delta-example')
  puts "Connected to #{address}"

  3.times do |i|
    msg = KubeMQ::PubSub::EventStoreMessage.new(channel: channel, metadata: "event #{i}", body: "data-#{i}")
    client.send_event_store(msg)
  end
  puts 'Pre-stored 3 events'
  sleep 1

  cancel = KubeMQ::CancellationToken.new
  delta_seconds = 60

  sub = KubeMQ::PubSub::EventsStoreSubscription.new(
    channel: channel,
    start_position: KubeMQ::PubSub::EventStoreStartPosition::START_AT_TIME_DELTA,
    start_position_value: delta_seconds
  )
  client.subscribe_to_events_store(sub, cancellation_token: cancel, on_error: lambda { |e|
    puts "Error: #{e.message}"
  }) do |event|
    puts "Received (within last #{delta_seconds}s): #{event.metadata}"
  end
  puts "Subscribed with START_AT_TIME_DELTA=#{delta_seconds}s"

  sleep 3
rescue KubeMQ::Error => e
  puts "KubeMQ error: #{e.message}"
ensure
  cancel&.cancel
  client&.close
  puts 'Done'
end

How It Works

• START_AT_TIME_DELTA replays events stored within the last N seconds.
• The start_position_value is the number of seconds to look back from the current time.
• Useful for "catch up on recent activity" scenarios without tracking sequence numbers.
• Review timeouts, channel names, and client IDs before running against shared environments.

Related

• Pattern overview
• Ruby SDK Reference
• Replay from Time
• Start from First