Realtime never establishes Postgres Changes subscription — realtime.subscription empty, 0 replication slots while client is actively subscribed (regression of #1747?)

[itszaidshah-tech]

Bug report

A hosted Pro project's client opens a Realtime websocket and sends phx_join with a postgres_changes config, but the Realtime service never registers the subscription server-side. realtime.subscription stays empty and no logical replication slot is ever created, even while a client is actively subscribed on screen. Live updates never arrive; the app has to fall back to polling.

This looks like the same class of issue as #1747 (closed, "intermittent subscribe failures after idle / replication slot missing") and the still-open #1414 ("CHANNEL_ERROR after a few hours"), but here the subscription is never successfully established, not just intermittently.

Environment

Supabase hosted, Pro plan
Postgres-side fully configured and verified (see diagnostics)
Client: Phoenix v2 websocket protocol, phx_join with postgres_changes (event: UPDATE, schema: public, table: posts), heartbeat + exponential-backoff reconnect

Postgres-side diagnostics (all correct)
-- wal_level = logical
-- max_replication_slots = 5, max_wal_senders = 5 (0 in use)
SELECT name, setting FROM pg_settings
WHERE name IN ('wal_level','max_replication_slots','max_wal_senders');

-- publication: pubinsert/pubupdate/pubdelete all true, 8 tables
SELECT pubname, pubinsert, pubupdate, pubdelete FROM pg_publication
WHERE pubname='supabase_realtime';

-- every published table: REPLICA IDENTITY FULL + RLS enabled ✓

-- realtime schema healthy, migrations current, message partitions
-- auto-provisioned for upcoming days (Realtime infra is reaching the DB)
SELECT max(version) FROM realtime.schema_migrations;

The problem — measured while a client is actively subscribed on screen:

SELECT
(SELECT count() FROM realtime.subscription) AS active_subscriptions, -- 0
(SELECT count() FROM pg_replication_slots WHERE slot_name LIKE 'supabase_realtime%') AS rt_slots, -- 0
(SELECT count() FROM pg_stat_replication) AS walsenders, -- 0
(SELECT count() FROM pg_stat_activity WHERE backend_type='walsender') AS walsender_backends; -- 0
realtime.subscription = 0 and pg_replication_slots = 0 every time, regardless of which screen/channel is open. Earlier, two supabase_realtime% slots were briefly observed active=true for a couple of minutes, then disappeared with no client change — i.e. the channel works occasionally then stops, and now does not register at all.

Expected

When a client successfully joins a postgres_changes channel, realtime.subscription should have a row for that subscription and a logical replication slot should be created/active for as long as the client is subscribed.

Actual

The websocket connects, phx_join is sent, but no subscription row and no replication slot are ever created. No client-side error is reliably surfaced (no CHANNEL_ERROR), it simply never goes live.

Questions

Is this a recurrence/regression of #1747, or a separate failure mode where phx_join for postgres_changes is accepted at the socket level but never materializes a realtime.subscription / replication slot?
What server-side state should we capture during a failed join to give you something actionable (relevant realtime.* tables, logs to request from support)?
Is there a known condition where the Realtime node accepts the websocket but fails to create the subscription/slot silently (no CHANNEL_ERROR to the client)?
Happy to provide more diagnostics or logs on request.

Thanks in advance

• I confirm this is a bug with Supabase, not with my own application.
• I confirm I have searched the Docs, GitHub Discussions, and Discord.

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