Re: PG 10 release notes

On 2017-05-04 20:46:24 -0400, Bruce Momjian wrote:
> On Thu, May 4, 2017 at 05:09:40PM -0700, Andres Freund wrote:
> > > > I would not in any way refer to logical decoding as being only a proof
> > > > of concept, even before logical replication.
> > >
> > > The community ships a reliable logical _encoding_, and a test logical
> > > _decoding_.
> >
> > Yes, so what? What you said is "I didn't think logical decoding was
> > really more than a proof-of-concept until now", which is plainly wrong,
> > given I know a significant number of users using it in production. Some
> > of them are well known & large enterprises, and it's used to enable
> > critical things.
>
> I am getting tired of saying this. When I am writing the release notes,
> I am trying to figure out how it affects our shipped code, and the only
> "decoding" I know of is test_decoding.

Then ask for input instead of saying uninformed stuff like "I didn't
think logical decoding was really more than a proof-of-concept". That's
what people are complaining about, not that you're not
all-knowledgeable. I agree with you - and wrote that previously - that
the specific change is not necessarily worthwhile to be mentioned on its
own, I don't see how that makes your various statements in this
subthread ok.

My message was this:
> https://www.postgresql.org/message-id/a6d13cf7-fbf8-913c-2353-f149c6f95fdc%402ndquadrant.com
> >
> >> Or the ability of logical decoding to follow timeline switches.
> >
> > I didn't think logical decoding was really more than a proof-of-concept
> > until now.
>
> Now, if the "encoding"

There's not really a "encoding" part of this. The decoding refers to
decoding the WAL into something externally usable.

> I assume it is this commit:

That, and
commit 24c5f1a103ce6656a5cb430d9a996c34e61ab2a5
Author: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Date: 2016-03-30 20:07:05 -0300

Enable logical slots to follow timeline switches

When decoding from a logical slot, it's necessary for xlog reading to be
able to read xlog from historical (i.e. not current) timelines;
otherwise, decoding fails after failover, because the archives are in
the historical timeline. This is required to make "failover logical
slots" possible; it currently has no other use, although theoretically
it could be used by an extension that creates a slot on a standby and
continues to replay from the slot when the standby is promoted.

This commit includes a module in src/test/modules with functions to
manipulate the slots (which is not otherwise possible in SQL code) in
order to enable testing, and a new test in src/test/recovery to ensure
that the behavior is as expected.

Author: Craig Ringer
Reviewed-By: Oleksii Kliukin, Andres Freund, Petr Jelínek