Hi,
On 11/21/23 6:16 AM, Amit Kapila wrote:
On Mon, Nov 20, 2023 at 6:51 PM Drouvot, Bertrand
<bertranddrouvot...@gmail.com> wrote:
As far the 'i' state here, from what I see, it is currently useful for:
1. Cascading standby to not sync slots with state = 'i' from
the first standby.
2. Easily report Slots that did not catch up on the primary yet.
3. Avoid inactive slots to block "active" ones creation.
So not creating those slots should not be an issue for 1. (sync are
not needed on cascading standby as not created on the first standby yet)
but is an issue for 2. (unless we provide another way to keep track and report
such slots) and 3. (as I think we should still need to reserve WAL).
I've a question: we'd still need to reserve WAL for those slots, no?
If that's the case and if we don't call ReplicationSlotCreate() then
ReplicationSlotReserveWal()
would not work as MyReplicationSlot would be NULL.
Yes, we need to reserve WAL to see if we can sync the slot. We are
currently creating an RS_EPHEMERAL slot and if we don't explicitly
persist it when we can't sync, then it will be dropped when we do
ReplicationSlotRelease() at the end of synchronize_one_slot(). So, the
loss is probably, the next time we again try to sync the slot, we need
to again create it and may need to wait for newer restart_lsn on
standby
Yeah, and doing so we'd reduce the time window to give the slot a chance
to catch up (as opposed to create it a single time and maintain an 'i' state).
which could be avoided if we have the slot in 'i' state from
the previous run.
Right.
I don't deny the importance of having 'i'
(initialized) state but was just trying to say that it has additional
code complexity.
Right, and I think it's worth it.
OTOH, having it may give better visibility to even
users about slots that are not active (say manually created slots on
the primary).
Agree.
All that being said, on my side I'm +1 on keeping the 'i' state behavior
as it is implemented currently (would be happy to hear others' opinions too).
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
