Re: Free indexed_tlist memory explicitly within set_plan_refs()

On Sun, May 24, 2015 at 6:17 PM, Peter Geoghegan <pg@heroku.com> wrote:
> Attached patch adds such a pfree() call.

Attached, revised version incorporates this small fix, while adding an
additional big fix, and a number of small style tweaks.

This is mainly concerned with fixing the bug I was trying to fix when
I spotted the minor pfree() issue:

postgres=# insert into upsert (key, val) values('Foo', 'Bar') on
conflict (key) do update set val = excluded.val where excluded.* is
not null;
ERROR:  XX000: variable not found in subplan target lists
LOCATION:  fix_join_expr_mutator, setrefs.c:2003
postgres=# insert into upsert (key, val) values(('Foo', 'Bar') on
conflict (key) do update set val = excluded.val where excluded.ctid is
not null;
ERROR:  XX000: variable not found in subplan target lists
LOCATION:  fix_join_expr_mutator, setrefs.c:2003

The first query shown should clearly finish processing by the
optimizer without raising this error message (execution should work
correctly too, of course). The second query shown should fail with a
user visible error message about referencing the excluded
pseudo-relation's ctid column not making sense.

The basic problem is that there wasn't much thought put into how the
excluded pseudo-relation's "reltargetlist" is generated -- it
currently comes from a call to expandRelAttrs() during parse analysis,
which, on its own, doesn't allow whole row Vars to work.

One approach to fixing this is to follow the example of RETURNING
lists with references to more than one relation:
preprocess_targetlist() handles this by calling pull_var_clause() and
making new TargetEntry entries for Vars found to not be referencing
the target (and not already in the targetlist for some other reason).
Another approach, preferred by Andres, is to have query_planner() do
more. I understand that the idea there is to make excluded.* closer to
a regular table, in that it can be expected to have a baserel, and
within the executor we have something closer to a bona-fide scan
reltargetlist, that we can expect to have all Vars appear in. This
should be enough to make the reltargetlist have the appropriate Vars
more or less in the regular course of planning, including excluded.*
whole row Vars.  To make this work we could call
add_vars_to_targetlist(), and call add_base_rels_to_query()  and then
build_base_rel_tlists() within query_planner() (while moving a few
other things around).

However, the ordering dependencies within query_planner() seemed quite
complicated to me, and I didn't want to modify such an important
routine just to fix this bug. RETURNING seemed like a perfectly good
precedent to follow, so that's what I did. Now, it might have been
that  I misunderstood Andres when we discussed this problem on
Jabber/IM, but ISTM that the second idea doesn't have much advantage
over the first (I'm sure that Andres will be able to explain what he'd
like to do better here -- it was a quick conversation). I did
prototype the second approach, and the code footprint of what I have
here (the first approach) seems lower than it would have to be with
the second. Besides, I didn't see a convenient choke point to reject
system column references with the second approach. Attached patch
fixes the bug using the first approach. Tests were added demonstrating
that the cases above are fixed.

A second attached patch fixes another, largely independent bug. I
noticed array assignment with ON CONFLICT DO UPDATE was broken. See
commit message for full details.

Thoughts?
--
Peter Geoghegan