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* Re: find replication slots that "belong" to a publication
@ 2025-04-06 13:36 Justin <[email protected]>
2025-04-07 10:16 ` Re: find replication slots that "belong" to a publication Willy-Bas Loos <[email protected]>
0 siblings, 1 reply; 5+ messages in thread
From: Justin @ 2025-04-06 13:36 UTC (permalink / raw)
To: Willy-Bas Loos <[email protected]>; +Cc: pgsql-general <[email protected]>
On Fri, Apr 4, 2025 at 4:58 AM Willy-Bas Loos <[email protected]> wrote:
> Hi!
>
> I'm looking for a way to find out if there are still replication slots
> active for a publication before dropping the publication in an automated
> way. The idea is that the publication is thought not to be needed any
> longer, but we want to make sure.
>
> I'm having trouble finding a link between a publication, the subscriptions
> and the replication slots. Especially when you don't want to make
> assumptions about any subscriber nodes, so you are restricted to the
> publisher node.
>
> The best I could find was a query listed in pg_stat_activity that lists
> the slot name and the publication name:
> START_REPLICATION SLOT "my_slot" LOGICAL 5DD1/3E56D360 (proto_version '1',
> publication_names '"my_publication"')
>
> I don't like the idea of using string manipulation on such query strings
> to get the information I need. Postgres must have a way to compose this
> query.
> Can anyone tell me a way to find replication slots that belong to a
> publication?
>
> --
> Willy-Bas Loos
>
Hi Willy-Bas,
Logical replication slots appear in the views pg_stat_replication and
pg_replication_slots. Both views have the information you are looking for,
the difference is pg_stat_replication shows only the active slots. Keep in
mind Temporary Slots only live for the length of the session that created
it; the slot will appear in both views.
The bigger issue I think you are trying to address is when can a slot be
dropped safely. Once a logical replication slot is dropped there is no
recovery of the slot's lsn position. Probably the best way to decide if a
slot has been abandoned is how far behind it is. The pg_wal_lsn_diff can
be used to figure out how far behind a slot is
https://www.postgresql.org/docs/13/view-pg-replication-slots.html
https://www.postgresql.org/docs/13/monitoring-stats.html#MONITORING-PG-STAT-REPLICATION-VIEW
https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-BACKUP
Hope this answers your question
Justin
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: find replication slots that "belong" to a publication
2025-04-06 13:36 Re: find replication slots that "belong" to a publication Justin <[email protected]>
@ 2025-04-07 10:16 ` Willy-Bas Loos <[email protected]>
2025-04-07 13:31 ` Re: find replication slots that "belong" to a publication Laurenz Albe <[email protected]>
0 siblings, 1 reply; 5+ messages in thread
From: Willy-Bas Loos @ 2025-04-07 10:16 UTC (permalink / raw)
To: Justin <[email protected]>; +Cc: pgsql-general <[email protected]>
Hi Justin, thanks for your anwer!
My question is not so much about "can i drop a certain replication slot",
more about "does this publication still have any replication slots?". Or,
if you will: "what's the publication for this replication slot?".
I've double checked the views that you suggested, and I found that I can
relate the WAL sender processes to replication slots through
pg_replication_slots.active_pid .
I've also looked into replication origins.
But I can't find a link to the publication. And that's what I need to know.
Cheers,
Willy-Bas
On Sun, Apr 6, 2025 at 3:36 PM Justin <[email protected]> wrote:
> On Fri, Apr 4, 2025 at 4:58 AM Willy-Bas Loos <[email protected]> wrote:
>
>> Hi!
>>
>> I'm looking for a way to find out if there are still replication slots
>> active for a publication before dropping the publication in an automated
>> way. The idea is that the publication is thought not to be needed any
>> longer, but we want to make sure.
>>
>> I'm having trouble finding a link between a publication, the
>> subscriptions and the replication slots. Especially when you don't want to
>> make assumptions about any subscriber nodes, so you are restricted to the
>> publisher node.
>>
>> The best I could find was a query listed in pg_stat_activity that lists
>> the slot name and the publication name:
>> START_REPLICATION SLOT "my_slot" LOGICAL 5DD1/3E56D360 (proto_version
>> '1', publication_names '"my_publication"')
>>
>> I don't like the idea of using string manipulation on such query strings
>> to get the information I need. Postgres must have a way to compose this
>> query.
>> Can anyone tell me a way to find replication slots that belong to a
>> publication?
>>
>> --
>> Willy-Bas Loos
>>
>
> Hi Willy-Bas,
>
> Logical replication slots appear in the views pg_stat_replication and
> pg_replication_slots. Both views have the information you are looking for,
> the difference is pg_stat_replication shows only the active slots. Keep in
> mind Temporary Slots only live for the length of the session that created
> it; the slot will appear in both views.
>
> The bigger issue I think you are trying to address is when can a slot be
> dropped safely. Once a logical replication slot is dropped there is no
> recovery of the slot's lsn position. Probably the best way to decide if a
> slot has been abandoned is how far behind it is. The pg_wal_lsn_diff can
> be used to figure out how far behind a slot is
>
> https://www.postgresql.org/docs/13/view-pg-replication-slots.html
>
> https://www.postgresql.org/docs/13/monitoring-stats.html#MONITORING-PG-STAT-REPLICATION-VIEW
>
>
> https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-ADMIN-BACKUP
>
> Hope this answers your question
>
>
> Justin
>
--
Willy-Bas Loos
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: find replication slots that "belong" to a publication
2025-04-06 13:36 Re: find replication slots that "belong" to a publication Justin <[email protected]>
2025-04-07 10:16 ` Re: find replication slots that "belong" to a publication Willy-Bas Loos <[email protected]>
@ 2025-04-07 13:31 ` Laurenz Albe <[email protected]>
2025-04-07 20:32 ` Re: find replication slots that "belong" to a publication Willy-Bas Loos <[email protected]>
0 siblings, 1 reply; 5+ messages in thread
From: Laurenz Albe @ 2025-04-07 13:31 UTC (permalink / raw)
To: Willy-Bas Loos <[email protected]>; Justin <[email protected]>; +Cc: pgsql-general <[email protected]>
On Mon, 2025-04-07 at 12:16 +0200, Willy-Bas Loos wrote:
> My question is not so much about "can i drop a certain replication slot",
> more about "does this publication still have any replication slots?".
> Or, if you will: "what's the publication for this replication slot?".
>
> I've double checked the views that you suggested, and I found that I can relate
> the WAL sender processes to replication slots through pg_replication_slots.active_pid .
> I've also looked into replication origins.
>
> But I can't find a link to the publication. And that's what I need to know.
I don't think that there is a connection between a publication and a
replication slot. That connection is only made when a subscriber connects
and runs the START_REPLICATION command [1] and specifies the "pgoutput"
plugin with the "publication_names" option [2].
I don't think you can see that information reflected in a system view
on the primary. You'd have to query "pg_subscription" on the standby.
Yours,
Laurenz Albe
[1]: https://www.postgresql.org/docs/current/protocol-replication.html#PROTOCOL-REPLICATION-START-REPLICA...
[2]: https://www.postgresql.org/docs/current/protocol-logical-replication.html#PROTOCOL-LOGICAL-REPLICATI...
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: find replication slots that "belong" to a publication
2025-04-06 13:36 Re: find replication slots that "belong" to a publication Justin <[email protected]>
2025-04-07 10:16 ` Re: find replication slots that "belong" to a publication Willy-Bas Loos <[email protected]>
2025-04-07 13:31 ` Re: find replication slots that "belong" to a publication Laurenz Albe <[email protected]>
@ 2025-04-07 20:32 ` Willy-Bas Loos <[email protected]>
2025-04-08 05:53 ` Re: find replication slots that "belong" to a publication Laurenz Albe <[email protected]>
0 siblings, 1 reply; 5+ messages in thread
From: Willy-Bas Loos @ 2025-04-07 20:32 UTC (permalink / raw)
To: Laurenz Albe <[email protected]>; +Cc: Justin <[email protected]>; pgsql-general <[email protected]>
Hi Laurenz,
Thanks for answering!
I find it very strange, because the publication is needed to make a
subscription, which makes the slot.
Thanks for looking into it and helping me understand.
Cheers!
Willy-Bas Loos
On Mon, Apr 7, 2025 at 3:31 PM Laurenz Albe <[email protected]>
wrote:
> On Mon, 2025-04-07 at 12:16 +0200, Willy-Bas Loos wrote:
> > My question is not so much about "can i drop a certain replication
> slot",
> > more about "does this publication still have any replication slots?".
> > Or, if you will: "what's the publication for this replication slot?".
> >
> > I've double checked the views that you suggested, and I found that I can
> relate
> > the WAL sender processes to replication slots through
> pg_replication_slots.active_pid .
> > I've also looked into replication origins.
> >
> > But I can't find a link to the publication. And that's what I need to
> know.
>
> I don't think that there is a connection between a publication and a
> replication slot. That connection is only made when a subscriber connects
> and runs the START_REPLICATION command [1] and specifies the "pgoutput"
> plugin with the "publication_names" option [2].
>
> I don't think you can see that information reflected in a system view
> on the primary. You'd have to query "pg_subscription" on the standby.
>
> Yours,
> Laurenz Albe
>
>
> [1]:
> https://www.postgresql.org/docs/current/protocol-replication.html#PROTOCOL-REPLICATION-START-REPLICA...
> [2]:
> https://www.postgresql.org/docs/current/protocol-logical-replication.html#PROTOCOL-LOGICAL-REPLICATI...
>
--
Willy-Bas Loos
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: find replication slots that "belong" to a publication
2025-04-06 13:36 Re: find replication slots that "belong" to a publication Justin <[email protected]>
2025-04-07 10:16 ` Re: find replication slots that "belong" to a publication Willy-Bas Loos <[email protected]>
2025-04-07 13:31 ` Re: find replication slots that "belong" to a publication Laurenz Albe <[email protected]>
2025-04-07 20:32 ` Re: find replication slots that "belong" to a publication Willy-Bas Loos <[email protected]>
@ 2025-04-08 05:53 ` Laurenz Albe <[email protected]>
0 siblings, 0 replies; 5+ messages in thread
From: Laurenz Albe @ 2025-04-08 05:53 UTC (permalink / raw)
To: Willy-Bas Loos <[email protected]>; +Cc: Justin <[email protected]>; pgsql-general <[email protected]>
On Mon, 2025-04-07 at 22:32 +0200, Willy-Bas Loos wrote:
> I find it very strange, because the publication is needed to make a subscription, which makes the slot.
Right, but that information is only on the subscriber.
Yours,
Laurenz Albe
^ permalink raw reply [nested|flat] 5+ messages in thread
end of thread, other threads:[~2025-04-08 05:53 UTC | newest]
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-- links below jump to the message on this page --
2025-04-06 13:36 Re: find replication slots that "belong" to a publication Justin <[email protected]>
2025-04-07 10:16 ` Willy-Bas Loos <[email protected]>
2025-04-07 13:31 ` Laurenz Albe <[email protected]>
2025-04-07 20:32 ` Willy-Bas Loos <[email protected]>
2025-04-08 05:53 ` Laurenz Albe <[email protected]>
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