Hi, On 2023-12-21 16:08:48 +0530, shveta malik wrote: > On Thu, Dec 21, 2023 at 3:10 PM Andres Freund <and...@anarazel.de> wrote: > > > > 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. > > Thanks for the feedback. But do you mean that we replace existing > 'conflicting' column with 'cause' in both the function and view > (pg_get_replication_slots() and pg_replication_slots)? Or do you mean > that we expose 'cause' from pg_get_replication_slots() and use that to > display 'conflicting' in pg_replication_slots view?
I'm not entirely sure I understand the difference - just whether we add one new column or replace the existing 'conflicting' column? I can see arguments for either. A conflicting column where NULL indicates no conflict, and other values indicate the reason for the conflict, doesn't seem too bad. > And if we plan to return/display cause from either function or view, > then shall it be enum 'ReplicationSlotInvalidationCause' or > description/text corresponding to enum? We clearly can't just expose the numerical value for a C enum. So it has to be converted to something SQL representable. > In the other feature being discussed "Synchronize slots from primary > to standby" [1] , there is a requirement to replicate invalidation > cause of slot from the primary to standby and thus it is needed in > enum form there. And thus there was a suggestion earlier to have the > function return enum-value and let the view display it as > text/description to the user. So kindly let us know your thoughts. > > [1] - > https://www.postgresql.org/message-id/514f6f2f-6833-4539-39f1-96cd1e011...@enterprisedb.com Can you point me to a more specific message for that requirement? It seems pretty odd to me. Your link goes to the top of a 400 message thread, I don't have time to find one specific design point in that... Greetings, Andres