Module: Pgbus::Client::EnsureStreamQueue

Included in:
Pgbus::Client
Defined in:
lib/pgbus/client/ensure_stream_queue.rb

Overview

Idempotent stream-queue setup. Creates the PGMQ queue (delegating to ‘ensure_queue` which already handles schema bootstrap and dedup), overrides the NOTIFY throttle to 0 so every broadcast fires its own NOTIFY, and adds an `msg_id` index on the archive table that PGMQ does not ship with.

PGMQ’s archive tables (‘pgmq.a_<name>`) only carry an `archived_at` index by default. `Client#read_after`’s replay query filters by ‘WHERE msg_id > $1`, which becomes a sequential scan once the archive grows past a few thousand rows. We add the index here, scoped to stream queues only, so users with chat-history-style retention don’t hit a performance cliff.

Called from ‘Pgbus.stream(name).broadcast(…)` on first publish per stream and from the streamer on first subscription per stream.

Instance Method Summary collapse

Instance Method Details

#ensure_stream_queue(stream_name) ⇒ Object 



21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
 
# File 'lib/pgbus/client/ensure_stream_queue.rb', line 21

def ensure_stream_queue(stream_name)
  ensure_queue(stream_name)
  full_name = config.queue_name(stream_name)

  # PGMQ's default NOTIFY throttle is 250ms — meant to coalesce
  # high-frequency worker queue inserts. Streams are latency-
  # sensitive and need every broadcast to fire a NOTIFY, even
  # when several are batched within a single millisecond.
  # Override the throttle to 0 specifically for stream queues.
  # Use the idempotent path to avoid deadlocks when multiple
  # processes race to set up the same stream queue.
  synchronized { enable_notify_if_needed(full_name, 0) }

  # CREATE INDEX IF NOT EXISTS is idempotent in Postgres but still
  # requires a roundtrip and a brief ACCESS SHARE lock on the archive
  # table. Broadcast-per-after_commit loops can hit this 1000x/sec on
  # the same stream, so memoize per-process after the first success.
  return if @stream_indexes_created[stream_name]

  sanitized = QueueNameValidator.sanitize!(full_name)
  sql = <<~SQL
    CREATE INDEX IF NOT EXISTS a_#{sanitized}_msg_id_idx
    ON pgmq.a_#{sanitized} (msg_id)
  SQL

  synchronized do
    with_raw_connection do |conn|
      conn.exec(sql)
    end
  end

  @stream_indexes_created[stream_name] = true
end