logical replication - who is managing replication slots created automatically during initial sync

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From: Avi Weinberg <[email protected]>
To: pgsql-generallists.postgresql.org <[email protected]>
Subject: logical replication - who is managing replication slots created automatically during initial sync
Date: Tue, 27 Aug 2024 06:53:42 +0000
Message-ID: <DB9PR07MB7180EA18C0A832E3B59D18B8CB942@DB9PR07MB7180.eurprd07.prod.outlook.com> (raw)

Hi Experts

I have seen that logical replication slots created automatically by Postgres during initial sync (a slot per table), are marked as "wal_status = lost" and "active = false".
1.      Who is responsible for removing those faulty replication slots?
2.      Can a slot with "wal_status = lost" recover from this state?
3.      Do I need to drop the subscription in such a case?
4.      Are those replication slots that synchronize a single table each, use a connection from "max_connections" and replication slot from "max_logical_replication_slots"?
5.      If I sync many tables will it be better to increase the number of max_logical_replication_slots or to have some of the tables "wait" for other tables to complete and release the replication slot for them to use.

I'm using Postgres 15.2
slot_name   plugin  slot_type   datoid  database    temporary   active  active_pid  xmin    catalog_xmin    restart_lsn confirmed_flush_lsn wal_status  safe_wal_size   two_phase
pg_8034820_sync_8033089_7371741997992267844 pgoutput    logical 16707   aaa_db  FALSE   FALSE   NULL    NULL    295098502   NULL    D9/EB7317B0 lost    NULL    FALSE
pg_6839631_sync_6837833_7371741997992267844 pgoutput    logical 16707   aaa_db  FALSE   FALSE   NULL    NULL    288349892   NULL    D2/80068A78 lost    NULL    FALSE

Thanks!

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