Re: [BUG?] strange behavior in ALTER TABLE ... RENAME TO on inherited columns

(2010/01/28 6:58), Robert Haas wrote:
> On Wed, Jan 27, 2010 at 3:42 PM, Robert Haas<robertmhaas@gmail.com>  wrote:
>> On Wed, Jan 27, 2010 at 10:17 AM, KaiGai Kohei<kaigai@kaigai.gr.jp>  wrote:
>>> (2010/01/27 23:29), Robert Haas wrote:
>>>>
>>>> 2010/1/27 KaiGai Kohei<kaigai@ak.jp.nec.com>:
>>>>>
>>>>> The attached patch is revised one based on the V3 approach.
>>>>> The only difference from V3 is that it also applies checks on the
>>>>> AT_AlterColumnType option, not only renameatt().
>>>>
>>>> I think I was clear about what the next step was for this patch in my
>>>> previous email, but let me try again.
>>>>
>>>> http://archives.postgresql.org/pgsql-hackers/2010-01/msg02407.php
>>>>
>>>> See also Tom's comments here:
>>>>
>>>> http://archives.postgresql.org/pgsql-hackers/2010-01/msg00110.php
>>>>
>>>> I don't believe that either Tom or I are prepared to commit a patch
>>>> based on this approach, at least not unless someone makes an attempt
>>>> to do it the other way and finds an even more serious problem.  If
>>>> you're not interested in rewriting the patch along the lines Tom
>>>> suggested, then we should just mark this as Returned with Feedback and
>>>> move on.
>>>
>>> The V3/V5 patch was the rewritten one based on the Tom's comment, as is.
>>> It counts the expected inhcount at the first find_all_inheritors() time
>>> at once, and it compares the pg_attribute.attinhcount.
>>> (In actually, find_all_inheritors() does not have a capability to count
>>> the number of merged from a common origin, so I newly defined the
>>> find_all_inheritors_with_inhcount().)
>>>
>>> Am I missing something?
>>
>> Err... I'm not sure.  I thought I understood what the different
>> versions of this patch were doing, but apparently I'm all confused.
>> I'll take another look at this.
> 
> OK, I took a look at this.  It's busted:
> 
> test=# create table top (a integer);
> CREATE TABLE
> test=# create table upper1 () inherits (top);
> CREATE TABLE
> test=# create table upper2 () inherits (top);
> CREATE TABLE
> test=# create table lower1 () inherits (upper1, upper2);
> NOTICE:  merging multiple inherited definitions of column "a"
> CREATE TABLE
> test=# create table lower2 () inherits (upper1, upper2);
> NOTICE:  merging multiple inherited definitions of column "a"
> CREATE TABLE
> test=# create table spoiler (a integer);
> CREATE TABLE
> test=# create table bottom () inherits (lower1, lower2, spoiler);
> NOTICE:  merging multiple inherited definitions of column "a"
> NOTICE:  merging multiple inherited definitions of column "a"
> CREATE TABLE
> test=# alter table top rename a to b;
> ALTER TABLE
> test=# select * from spoiler;
> ERROR:  could not find inherited attribute "a" of relation "bottom"

Hmm, indeed, this logic (V3/V5) is busted.

The idea of V4 patch can also handle this case correctly, although it
is lesser in performance.
I wonder whether it is really unacceptable cost in performance, or not.
Basically, I assume ALTER TABLE RENAME/TYPE is not frequent operations,
and I don't think this bugfix will damage to the reputation of PostgreSQL.

Where should we go on the next?

Thanks,
-- 
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai@ak.jp.nec.com>