if Code.ensure_loaded?(Postgrex) do
defmodule Oban.Notifiers.Postgres do
@moduledoc """
A Postgres LISTEN/NOTIFY based Notifier.
> #### Connection Pooling {: .info}
>
> Postgres PubSub is fine for most applications, but it doesn't work with connection poolers
> like [PgBouncer][pgb] when configured in _transaction_ or _statement_ mode, which is
> standard. Notifications are required for some core Oban functionality, and you should
> consider using an alternative notifier such as `Oban.Notifiers.PG`.
## Usage
Specify the `Postgres` notifier in your Oban configuration:
config :my_app, Oban,
notifier: Oban.Notifiers.Postgres,
...
### Transactions and Testing
The notifications system is built on PostgreSQL's `LISTEN/NOTIFY` functionality. Notifications
are only delivered **after a transaction completes** and are de-duplicated before publishing.
Typically, applications run Ecto in sandbox mode while testing, but sandbox mode wraps each test
in a separate transaction that's rolled back after the test completes. That means the
transaction is never committed, which prevents delivering any notifications.
To test using notifications you must run Ecto without sandbox mode enabled, or use
`Oban.Notifiers.PG` instead.
[pgb]: https://www.pgbouncer.org/
"""
@behaviour Oban.Notifier
alias Oban.{Config, Notifier, Repo}
alias Postgrex.SimpleConnection, as: Simple
defstruct [
:conf,
:from,
:key,
channels: %{},
connected?: false,
listeners: %{}
]
@impl Oban.Notifier
def start_link(opts) do
name = Keyword.fetch!(opts, :name)
conf = Keyword.fetch!(opts, :conf)
state = struct!(__MODULE__, conf: conf)
conn_opts =
conf
|> Repo.config()
|> Keyword.put(:name, name)
|> Keyword.put_new(:auto_reconnect, true)
|> Keyword.put_new(:sync_connect, false)
Simple.start_link(__MODULE__, state, conn_opts)
end
@impl Oban.Notifier
def listen(server, channels) do
Simple.call(server, {:listen, self(), channels})
end
@impl Oban.Notifier
def unlisten(server, channels) do
Simple.call(server, {:unlisten, self(), channels})
end
## Server Callbacks
def init(state) do
put_state(state)
{:ok, state}
end
@impl Oban.Notifier
def notify(full_channel, payload, state) when is_binary(full_channel) do
listeners = Map.get(state.channels, full_channel, [])
Notifier.relay(state.conf, listeners, reverse_channel(full_channel), payload)
end
# This is a Notifier callback, but it has the same name and arity as SimpleConnection
def notify(server, channel, payload) when is_atom(channel) do
with %{conf: conf} <- get_state(server) do
full_channel = to_full_channel(channel, conf)
Repo.query(
conf,
"SELECT pg_notify($1, payload) FROM json_array_elements_text($2::json) AS payload",
[full_channel, payload]
)
:ok
end
end
def handle_connect(%{channels: channels} = state) do
state = %{state | connected?: true}
if map_size(channels) > 0 do
listens =
channels
|> Map.keys()
|> Enum.map_join("\n", &~s(LISTEN "#{&1}";))
query(listens, state)
else
{:noreply, state}
end
end
def handle_disconnect(%{} = state) do
{:noreply, %{state | connected?: false}}
end
def handle_call({:listen, pid, channels}, from, state) do
channels = Enum.map(channels, &to_full_channel(&1, state.conf))
new_channels = channels -- Map.keys(state.channels)
state =
state
|> put_listener(pid, channels)
|> put_channels(pid, channels)
if state.connected? and Enum.any?(new_channels) do
listens = Enum.map_join(new_channels, " \n", &~s(LISTEN "#{&1}";))
query(listens, %{state | from: from})
else
Simple.reply(from, :ok)
{:noreply, state}
end
end
def handle_call({:unlisten, pid, channels}, from, state) do
channels = Enum.map(channels, &to_full_channel(&1, state.conf))
state =
state
|> del_listener(pid, channels)
|> del_channels(pid, channels)
del_channels = channels -- Map.keys(state.channels)
if state.connected? and Enum.any?(del_channels) do
unlistens = Enum.map_join(del_channels, " \n", &~s(UNLISTEN "#{&1}";))
query(unlistens, %{state | from: from})
else
Simple.reply(from, :ok)
{:noreply, state}
end
end
def handle_info({:DOWN, _ref, :process, pid, _reason}, state) do
case Map.pop(state.listeners, pid) do
{{_ref, channel_set}, listeners} ->
state =
state
|> Map.put(:listeners, listeners)
|> del_channels(pid, MapSet.to_list(channel_set))
{:noreply, state}
{nil, _listeners} ->
{:noreply, state}
end
end
def handle_info(_message, state) do
{:noreply, state}
end
def handle_result(_results, %{from: from} = state) do
from && Simple.reply(from, :ok)
{:noreply, %{state | from: nil}}
end
## Helpers
defp put_state(state) do
Registry.update_value(Oban.Registry, {state.conf.name, Oban.Notifier}, fn _ -> state end)
end
defp get_state(server) do
[name] = Registry.keys(Oban.Registry, server)
case Oban.Registry.lookup(name) do
{_pid, state} -> state
nil -> {:error, RuntimeError.exception("no notifier running as #{inspect(name)}")}
end
end
defp query(statement, state) do
{:query, ["DO $$BEGIN ", statement, " END$$"], state}
end
defp to_full_channel(channel, %Config{prefix: prefix}) do
"#{prefix}.oban_#{channel}"
end
defp reverse_channel(full_channel) do
[_prefix, "oban_" <> shortcut] = String.split(full_channel, ".", parts: 2)
String.to_existing_atom(shortcut)
end
defp put_listener(%{listeners: listeners} = state, pid, channels) do
new_set = MapSet.new(channels)
listeners =
case Map.get(listeners, pid) do
{ref, old_set} ->
Map.replace!(listeners, pid, {ref, MapSet.union(old_set, new_set)})
nil ->
ref = Process.monitor(pid)
Map.put(listeners, pid, {ref, new_set})
end
%{state | listeners: listeners}
end
defp put_channels(state, pid, channels) do
listener_channels =
for channel <- channels, reduce: state.channels do
acc -> Map.update(acc, channel, [pid], &[pid | &1])
end
%{state | channels: listener_channels}
end
defp del_listener(%{listeners: listeners} = state, pid, channels) do
new_set = MapSet.new(channels)
listeners =
case Map.get(listeners, pid) do
{ref, old_set} ->
del_set = MapSet.difference(old_set, new_set)
if MapSet.size(del_set) == 0 do
Process.demonitor(ref)
Map.delete(listeners, pid)
else
Map.replace!(listeners, pid, {ref, del_set})
end
nil ->
listeners
end
%{state | listeners: listeners}
end
defp del_channels(state, pid, channels) do
listener_channels =
for channel <- channels, reduce: state.channels do
acc ->
acc = Map.update(acc, channel, [], &List.delete(&1, pid))
if Enum.empty?(acc[channel]), do: Map.delete(acc, channel), else: acc
end
%{state | channels: listener_channels}
end
end
end
