| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Michael Paquier <michael(at)paquier(dot)xyz> |
| Cc: | Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> |
| Subject: | Re: Track in pg_replication_slots the reason why slots conflict? |
| Date: | 2023-12-21 09:40:15 |
| Message-ID: | 20231221094015.bsrblo55laak7vhy@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2023-12-21 09:21:04 +0900, Michael Paquier wrote:
> While listening at Bertrand's talk about logical decoding on standbys
> last week at Prague, I got surprised by the fact that we do not
> reflect in the catalogs the reason why a conflict happened for a slot.
> There are three of them depending on ReplicationSlotInvalidationCause:
> - WAL removed.
> - Invalid horizon.
> - Insufficient WAL level.
It should be extremely rare to hit any of these other than "WAL removed", so
I'm not sure it's worth adding interface complexity to show them.
> ReplicationSlotCtl holds this information, so couldn't it be useful
> for monitoring purposes to know why a slot got invalidated and add a
> column to pg_get_replication_slots()? This could just be an extra
> text conflicting_reason, defaulting to NULL when there's nothing to
> see.
Extra columns aren't free from a usability perspective. IFF we do something, I
think it should be a single column with a cause.
Greetings,
Andres Freund
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