Re: Is it worth adding ReplicationSlot active_pid to ReplicationSlotPersistentData?

On 2021-Dec-01, Bharath Rupireddy wrote:

> The active_pid of ReplicationSlot structure, which tells whether a
> replication slot is active or inactive, isn't persisted to the disk
> i.e has no entry in ReplicationSlotPersistentData structure. Isn't it
> better if we add that info to ReplicationSlotPersistentData structure
> and persist to the disk? This will help to know what were the inactive
> replication slots in case the server goes down or crashes for some
> reason. Currently, we don't have a way to interpret the replication
> slot info in the disk but there's a patch for pg_replslotdata tool at
> [1]. This way, one can figure out the reasons for the server
> down/crash and figure out which replication slots to remove to bring
> the server up and running without touching the other replication
> slots.

I think the PIDs are log-worthy for sure, but it's not clear to me that
it is desirable to write them to the persistent state file. In case of
crashes, the log should serve just fine to aid root cause investigation
-- in fact even better than the persistent file, where the data would be
lost as soon as the next client acquires that slot.

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