Date: Tue, 19 Feb 2019 19:41:40 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: propagating replica identity to partitions
Message-ID: <20190219224140.GA14819@alvherre.pgsql>
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On 2019-Feb-19, Robert Haas wrote:

> On Tue, Feb 19, 2019 at 3:40 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > Maybe we should be using the inheritance marker in the command to note
> > whether to recurse to partitions?  That is, if you say
> >   ALTER TABLE ONLY parent SET REPLICA IDENTITY
> > then we don't recurse and just change the parent table and future
> > partitions, whereas if you leave out the ONLY then it does affect
> > existing partitions.
> >
> > However, I think TABLESPACE and any other property that involves
> > rewriting tables wholesale can reasonably be expected to behave
> > differently (w.r.t. recursing) from commands that just modify the
> > catalogs.  I think we already have such a distinction somewhere.
> 
> I don't really follow why that should be different, or why the user
> should be expected to know or care whether a particular property
> involves rewriting.

OK, let me concede that point -- it's not rewriting that makes things
act differently, but rather TABLESPACE (as well as some other things)
behave that way.  ALTER TABLE ... SET DATA TYPE is the obvious
counterexample.

The Notes section of ALTER TABLE says:

: The actions for identity columns (ADD GENERATED, SET etc., DROP IDENTITY), as
: well as the actions TRIGGER, CLUSTER, OWNER, and TABLESPACE never recurse to
: descendant tables; that is, they always act as though ONLY were specified.
: Adding a constraint recurses only for CHECK constraints that are not marked NO
: INHERIT.

Since REPLICA IDENTITY does not appear in this list, the documented
behavior is to recurse, per the description of the "name" parameter:

: The name (optionally schema-qualified) of an existing table to
: alter. If ONLY is specified before the table name, only that table
: is altered. If ONLY is not specified, the table and all its
: descendant tables (if any) are altered. Optionally, * can be
: specified after the table name to explicitly indicate that
: descendant tables are included.

I didn't come up with this on my own, as you imply.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services