From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Jeevan Ladhe <jeevan.ladhe@enterprisedb.com>,
        Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>,
        amul sul <sulamul@gmail.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Bug in pg_dump --table and --exclude-table for declarative
 partition table handling.
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Thu, 11 May 2017 09:13:56 -0400"
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Date: Thu, 11 May 2017 09:33:27 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, May 11, 2017 at 9:02 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> You could argue that it would be better for pg_dump to emit something
>> like
>> 
>> CREATE TABLE c (...);
>> ALTER TABLE c INHERIT p;
>> 
>> so that if p isn't around, at least c gets created.  And I think it
>> *would* be better, probably.  But if that isn't a new feature then
>> I don't know what is.  And partitioning really ought to track the
>> behavior of inheritance here.

> Hmm, I think that'd actually be worse, because it would break the use
> case where you want to restore the old contents of one particular
> inheritance child.  So you drop that child (but not the parent or any
> other children) and then do a selective restore of that one child.
> Right now that works fine, but it'll fail with an error if we try to
> create the already-extant parent.

Uh ... what in that is creating the already-extant parent?  What
I'm envisioning is simply that the TOC entry for the child table
contains those two statements rather than "CREATE TABLE c (...)
INHERITS (p)".  The equivalent thing for the partitioned case is
to use a separate ATTACH PARTITION command rather than naming the
parent immediately in the child's CREATE TABLE.  This is independent
of the question of how --table and friends ought to behave.

> I think one answer to the original complaint might be to add a new
> flag to pg_dump, something like --recursive-selection, maybe -r for
> short, which makes --table, --exclude-table, and --exclude-table-data
> cascade to inheritance descendents.

Yeah, you could do it like that.  Another way to do it would be to
create variants of all the selection switches, along the lines of
"--table-all=foo" meaning "foo plus its children".  Then you could
have some switches recursing and others not within the same command.
But maybe that's more flexibility than needed ... and I'm having a
hard time coming up with nice switch names, anyway.

Anyway, I'm still of the opinion that it's fine to leave this as a
future feature.  If we've gotten away without it this long for
inherited tables, it's unlikely to be critical for partitioned tables.

			regards, tom lane


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