# Broadcasting from the database

> Send Realtime Broadcast messages straight from Postgres with realtime.send and realtime.broadcast_changes, using triggers and private channels instead of Postgres Changes.

Source: https://supahost.app/kb/realtime-broadcast-from-database · Updated 2026-11-11

You can publish Realtime messages from SQL. `realtime.send()` sends any JSON payload to a topic, and `realtime.broadcast_changes()` sends a row change in a ready-made format. Call either from a trigger and every insert, update or delete reaches subscribed clients as a Broadcast message.

## Why use it instead of Postgres Changes

Postgres Changes checks RLS for every change and every subscriber. Database broadcast checks authorization once, when a client joins a channel, through policies on `realtime.messages`. You also choose the topic and the payload, so you can send only the fields clients need, or fan out one change to a specific topic such as `booking:381`.

## Send a custom message

```sql
select realtime.send(
  payload => jsonb_build_object('status', 'confirmed', 'booking_id', 381),
  event   => 'status-changed',
  topic   => 'booking:381',
  private => true
);
```

`private` defaults to `true`. A private message only reaches channels created with `config: { private: true }`; a public one only reaches public channels. They must match.

## Broadcast row changes with a trigger

This example sends every change to a booking to that booking's own topic.

```sql
create or replace function public.broadcast_booking_change()
returns trigger
language plpgsql
security definer
set search_path = ''
as $$
begin
  perform realtime.broadcast_changes(
    'booking:' || coalesce(new.id, old.id)::text, -- topic
    tg_op,                                         -- event name
    tg_op,                                         -- operation
    tg_table_name,
    tg_table_schema,
    new,
    old
  );
  return null;
end;
$$;

create trigger bookings_broadcast
after insert or update or delete on public.bookings
for each row execute function public.broadcast_booking_change();
```

## Allow users to receive it

Private channels need a `select` policy on `realtime.messages`. Here a guest can listen only to their own bookings' topics:

```sql
create policy "Guests receive their booking topics"
on realtime.messages for select
to authenticated
using (
  exists (
    select 1 from public.bookings b
    where b.guest_id = (select auth.uid())
      and 'booking:' || b.id::text = (select realtime.topic())
  )
);
```

Add only policies. Don't run `alter table` on `realtime.messages`; see [must be owner of table messages](/kb/realtime-must-be-owner-messages).

## Listen in the client

```js
await supabase.realtime.setAuth() // use the signed-in user's token

const channel = supabase
  .channel(`booking:${bookingId}`, { config: { private: true } })
  .on('broadcast', { event: 'UPDATE' }, ({ payload }) => {
    console.log('booking changed', payload)
  })
  .on('broadcast', { event: 'status-changed' }, ({ payload }) => {
    showStatus(payload.status)
  })
  .subscribe()
```

## Common problems

- **Nothing arrives:** a public channel listening for a private message (or the reverse), a topic typo, or no `select` policy for the user.
- **`CHANNEL_ERROR` on join:** the client isn't signed in, or no policy matches the topic.
- **The trigger errors:** `realtime.send` catches its own errors so it won't break your write, but a bug elsewhere in your trigger function will. Test it in Studio's SQL editor first.

## On SupaHost

Database broadcast works on SupaHost as upstream: each project's database has its own `realtime` schema and its own Realtime tenant. There's no dashboard switch to make a project accept private channels only, so treat any topic without a private flag as public. Broadcast messages are free on SupaHost; there are no per-message fees, though each project is limited to 5,000 events per second.

## Related

- [Broadcast](/docs/realtime/broadcast)
- [Realtime authorization](/docs/realtime/authorization)
- [Triggers](/docs/database/triggers)
- [Postgres Changes not firing](/kb/realtime-postgres-changes)