RE: speed up a logical replica setup

Dear Euler,

>> The possible solution would be
>> 1) allow to run pg_createsubscriber if standby is initially stopped .
>> I observed that pg_logical_createsubscriber also uses this approach.
>> 2) read GUCs via SHOW command and restore them when server restarts
>>
>3. add a config-file option. That's similar to what pg_rewind does.

Sorry, which pg_rewind option did you mention? I cannot find.
IIUC, -l is an only option which can accept the path, but it is not related with us.

Also, I'm not sure the benefit to add as new options. Basically it should be less.
Is there benefits than read via SHOW? Even if I assume the pg_resetwal has such
an option, the reason is that the target postmaster for pg_resetwal must be stopped.

>I expect
>that Debian-based installations will have this issue.

I'm not familiar with the Debian-env, so can you explain the reason?

>It was not a good idea if you want to keep the postgresql.conf outside PGDATA.
>I mean you need extra steps that can be error prone (different settings between
>files).

Yeah, if we use my approach, users who specify such GUCs may not be happy.
So...based on above discussion, we should choose either of below items. Thought?

a)
enforce the standby must be *stopped*, and options like config_file can be specified via option.
b)
enforce the standby must be *running*, options like config_file would be read via SHOW command.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/global/