Re: [HACKERS] Create replication slot in pg_basebackup if requestedand not yet present

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От Michael Banck
Тема Re: [HACKERS] Create replication slot in pg_basebackup if requestedand not yet present
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Msg-id 1504852916.25868.16.camel@credativ.de
обсуждение исходный текст
Ответ на Re: [HACKERS] Create replication slot in pg_basebackup if requestedand not yet present  (Peter Eisentraut <peter.eisentraut@2ndquadrant.com>)
Ответы Re: [HACKERS] Create replication slot in pg_basebackup if requestedand not yet present  (Michael Banck <michael.banck@credativ.de>)
Список pgsql-hackers
Hi,

Am Mittwoch, den 06.09.2017, 12:22 -0400 schrieb Peter Eisentraut:
> On 8/18/17 05:28, Michael Banck wrote:
> > > > Rebased, squashed and slighly edited version attached. I've added this
> > > > to the 2017-07 commitfest now as well:
> > > > 
> > > > https://commitfest.postgresql.org/14/1112/
> > > 
> > > Can you rebase this past some conflicting changes?
> > 
> > Thanks for letting me know, PFA a rebased version.
> 
> I have reviewed the thread so far.  I think there is general agreement
> that something like this would be good to have.
> 
> I have not found any explanation, however, why the "if not exists"
> behavior is desirable, let alone as the default.  I can only think of
> two workflows here:  Either you have scripts for previous PG versions
> that create the slot externally, in which can you omit --create, or you
> use the new functionality to have pg_basebackup create the slot.  I
> don't see any use for pg_basebackup to opportunistically use a slot if
> it happens to exist.  Even if there is one, it should not be the
> default.  So please change that.

Ok, I tried to research why that was the case and couldn't find any
trace of a discussion either.

So we should just error out in CreateReplicationSlot() in case a slot
exists, right? I think having yet another option like --create-if-not-
exists does not sound needed from what you wrote above.

> A minor point, I suggest to print the message about the replication slot
> being created *after* the slot has been created.  This aligns with how
> logical replication subscriptions work.  

Ok.

> I don't see the need for printing a message about temporary slots. 
> Since they are temporary, they will go away automatically, so there is
> nothing the user needs to know there.

Ok. I thought I'd remembered some request around having this reported
always (maybe from Magnus), but I couldn't find anything in the prior
discussions either.

If we don't print the message for temporary slots, then the
CreateReplicationSlot() refactoring and the addition of the
temp_replication_slot argument would be no longer needed, or is this
something useful on its own?


Thanks,

Michael

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Michael Banck
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