Re: speed up a logical replica setup

On Wed, May 22, 2024, at 12:16 PM, Euler Taveira wrote:
> I'll summarize all issues as soon as I finish the review of sync slot support. I
> think we should avoid new development if we judge that the item can be
> documented as a limitation for this version. Nevertheless, I will share patches
> so you can give your opinion on whether it is an open item or new development.

Here it is a patch series to fix the issues reported in recent discussions. The
patches 0001 and 0003 aim to fix the buildfarm issues. The patch 0002 removes
synchronized failover slots on subscriber since it has no use. I also included
an optional patch 0004 that improves the usability by checking both servers if
it already failed in any subscriber check.

As I said in this previous email I decided to remove the logic that reacts for
an issue on primary. We can reintroduce another code later if/when we have a
better way to check the recovery progress. It will rely on the recovery_timeout
and it adds recovery_timeout equals to PG_TEST_TIMEOUT_DEFAULT to let the
animals control how long it should wait for the recovery.

Since some animals reported some issues in the check_publisher routine that
checks if the primary_slot_name is in use on primary, this logic was removed
too (patch 0003). We could introduce a way to keep trying this test but the
conclusion is that it is not worth it and if the primary_slot_name does not
exist (due to a setup error), pg_createsubscriber will log an error message and
continue.

The 0002 removes any failover slots that remains on subscriber. Talking about
terminology, I noticed that slotsync.c uses "logical failover slots" and
"failover logical slots", I think the latter sounds better but I'm not a native
speaker. I also don't know if we use a short terminology like "failover slots"
"failover replication slots" or "failover logical replication slots". IMO we
can omit "logical" because "failover" infers it is a logical replication slot.
I'm also not sure about omitting "replication". It is not descriptive enough. I
prefer "failover replication slots".

Before sending this email I realized that I did nothing about physical
replication slots on the standby. I think we should also remove them too
unconditionally.

--
Euler Taveira
EDB https://www.enterprisedb.com/