Re: I'm surprised to see the word master here

Greetings,

* Bruce Momjian (bruce(at)momjian(dot)us) wrote:
> On Wed, Oct 2, 2019 at 03:04:55PM -0400, Stephen Frost wrote:
> > I don't agree with this claim. While we could argue about if a hot
> > standby is considered "active" or not, the vast majority of the world
> > considers "active/active" to actually be where you can use the two
> > systems interchangably, including being able to write to both. As such,
> > I disagree with this claim- while perhaps you could make an argument
> > that it's "technically" correct, it's not how the terms are used in
> > practice and saying active/active instead would be well understood by
> > the community and industry at large.
>
> With master/standby-replica-slave, it is clear what multi-master is, and
> what master/replica is. If you start using active-active, is it
> active/replica? The full choices are:

I'm a bit confused, as I thought that I explained exactly my thoughts on
this in the paragraph you quoted.

No, active/active isn't "active/replica", it's what we call today
"multi-master".

I'm also at a loss as to why we're discussing what to call 'master/
master' here since we don't actually use the term 'master/master' in our
docs at all today that I can see. There's one place where we talk about
'Multimaster' and that's here:

https://www.postgresql.org/docs/current/different-replication-solutions.html

> Whatever terms we use, it would be nice to use the same term for the
> multi-master as for master/replica. Using active-active and
> primary/replica just seems odd. Multi-primary? Seems odd since primary
> suggests one, though multiple master seems odd too, i.e., more than one
> master. Multi-active seems the most logical, or active-active, but then
> active-replica seems odd because it suggests the repica is not active,
> i.e. does nothing. Is no clear logical terminology possible?

I'm confused here again. Why would we want to use the same term for two
primaries that are working together as we would for a primary and a
replica...? Those are two quite different setups, and, at least in my
experience, 'active-active' only applies to the case where you have two
primaries involved.

In any case, removing the term 'master' from:

https://www.postgresql.org/docs/current/warm-standby.html

doesn't actually run into any of these issues because we don't say
'Multimaster' or 'master/master' or anything like that on that page, we
just keep going back and forth between 'master' and 'primary' without
any real reason for doing so. There's also some areas which could use
clarification, like:

In standby mode, the server continuously applies WAL received from the
master server.

Which isn't entirely accurate- the server continuously applies WAL
received from the primary, or the upstream standby it is connected to,
though we could possibly just include a reference down to Cacading
Replication to clarify that.

Of course, down in cascading replication we actually say:

which eventually links to a single master/primary server.

Which just re-enforces that we're pretty confused in that page regarding
the language/distinction between those two.

Coming back around to:

https://www.postgresql.org/docs/current/different-replication-solutions.html

and the "master/Multimaster" references there- most of the "master" ones
can be changed directly to "primary" (and most of the "standby" one
should really probably be "replica"... that's a different task though,
to go through and clean up that, but also a worthwhile one, imv). The
"Multimaster" references could go to "active-active" without any loss in
readability or understanding, imv, and we further explain each case in
the description of those anyway.

Though I have to say that I take some exception with the general
"Multimaster" or "active-active" concept being applied to offline /
periodically sync'd systems like when you have laptops or such involved,
but that's a different issue.

Thanks,

Stephen