Re: libpq options

On Fri, Mar 2, 2018 at 2:50 AM, Michael Paquier <michael(at)paquier(dot)xyz> wrote:

> On Thu, Mar 01, 2018 at 01:35:54AM -0800, Andres Freund wrote:
> > On 2017-11-25 19:05:54 +0900, Michael Paquier wrote:
> >> A Boolean value of <literal>true</literal> tells the backend
> >> + to go into walsender mode, wherein a small set of replication
> commands
> >> + can be issued instead of SQL statements.
> >
> > This actually is wrong now I think. Petr?
>
> On more or less HEAD:
> $ psql -X -d "replication=1 dbname=postgres"
> postgres=# create table aa (a int);
> ERROR: cannot execute SQL commands in WAL sender for physical replication
> $ psql -X -d "replication=database dbname=postgres"
> postgres=# create table aa (a int);
> CREATE TABLE
>
> So one needs to use replication=database in order to be able to issue
> normal SQL statements, while replication=true enforces physical
> replication where this cannot happen (no connection to a specified
> database).
>

To nitpick:

+ protocol. A Boolean value of <literal>true</literal> tells the
backend

We don't really have boolean values here, do we? It's just the string true
that's treated as a boolean by the backend. It just sounds really weird to
me when written that way. Particularly since the next sentence talks about
passing "database" as the same thing.

I know that's pretty much nitpicking, but I want to make sure I haven't
actually missed/forgotten how some part of that one is handled..

It also talks separately about "going into walsender mode" (=physical
replication) and "instructs the walsender to connect to the database". I
think that's a bit confusing. I suggest just calling it "physical
replication mode" and "logical replication mode", and not bother mentioning
walsender since that's quite internal.

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
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