Re: speed up a logical replica setup

On Thu, Mar 21, 2024, at 10:33 AM, vignesh C wrote:
> If we commit this we might not be able to change the way the option
> behaves once the customers starts using it. How about removing these
> options in the first version and adding it in the next version after
> more discussion.

We don't need to redesign this one if we want to add a format string in a next
version. A long time ago, pg_dump started to accept pattern for tables without
breaking or deprecating the -t option. If you have 100 databases and you don't
want to specify the options or use a script to generate it for you, you also
have the option to let pg_createsubscriber generate the object names for you.
Per my experience, it will be a rare case.

> Currently dry-run will do the check and might fail on identifying a
> few failures like after checking subscriber configurations. Then the
> user will have to correct the configuration and re-run then fix the
> next set of failures. Whereas the suggest-config will display all the
> optimal configuration for both the primary and the standby in a single
> shot. This is not a must in the first version, it can be done as a
> subsequent enhancement.

Do you meant publisher, right? Per order, check_subscriber is done before
check_publisher and it checks all settings on the subscriber before exiting. In
v30, I changed the way it provides the required settings. In a previous version,
it fails when it found a wrong setting; the current version, check all settings
from that server before providing a suitable error.

pg_createsubscriber: checking settings on publisher
pg_createsubscriber: primary has replication slot "physical_slot"
pg_createsubscriber: error: publisher requires wal_level >= logical
pg_createsubscriber: error: publisher requires 2 replication slots, but only 0 remain
pg_createsubscriber: hint: Consider increasing max_replication_slots to at least 3.
pg_createsubscriber: error: publisher requires 2 wal sender processes, but only 0 remain
pg_createsubscriber: hint: Consider increasing max_wal_senders to at least 3.

If you have such an error, you will fix them all and rerun using dry run mode
again to verify everything is ok. I don't have a strong preference about it. It
can be changed easily (unifying the check functions or providing a return for
each of the check functions).

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