Re: [Postgres-xc-developers] Query Planning bug ?

[Tomonari K. <kat...@po...>]

Hi Ashutosh,

Thank you for the response.

(2013/06/12 14:43), Ashutosh Bapat wrote:
 >> Hi,
 >> >
 >> > I've investigated this problem(BUG:3614369).
 >> >
 >> > I caught the cause of it, but I can not
 >> > find where to fix.
 >> >
 >> > The problem occurs when "pgxc_collect_RTE_walker" is called 
infinitely.
 >> > It seems that rtable(List of RangeTable) become cyclic List.
 >> > I'm not sure where the List is made.
 >> >
 >> >
 > I guess, we are talking about EXECUTE DIRECT statement that you have
 > mentioned earlier.

Yes, that's right.
I'm talking about EXECUTE DIRECT statement like below.
  ---
  EXECUTE DIRECT ON (data1) $$
  SELECT
  count(*)
  FROM
  (SELECT * FROM pg_locks l LEFT JOIN
  (SELECT * FROM pg_stat_activity) s ON l.database = s.datid) a
  $$
  ---

 > The function pgxc_collect_RTE_walker() is a recursive
 > function. The condition to end the recursion is if the given node is 
NULL.
 > We have to look at if that condition is met and if not why.
 >
I investigated it deeper, and I noticed that
the infinitely loop happens at the function "range_table_walker()".

Please see below trace.
===========================
Breakpoint 1, range_table_walker (rtable=0x15e7968, walker=0x612c70 
<pgxc_collect_RTE_walker>, context=0x7fffd2de31c0,
     flags=0) at nodeFuncs.c:1908
1908    in nodeFuncs.c

(gdb) p *rtable
$10 = {type = T_List, length = 5, head = 0x15e7998, tail = 0x15e9820}
(gdb) p *rtable->head
$11 = {data = {ptr_value = 0x15e79b8, int_value = 22968760, oid_value = 
22968760}, next = 0x15e8190}
(gdb) p *rtable->head->next
$12 = {data = {ptr_value = 0x15e81b0, int_value = 22970800, oid_value = 
22970800}, next = 0x15e8988}
(gdb) p *rtable->head->next->next
$13 = {data = {ptr_value = 0x15e89a8, int_value = 22972840, oid_value = 
22972840}, next = 0x15e9018}
(gdb) p *rtable->head->next->next->next
$14 = {data = {ptr_value = 0x15e9038, int_value = 22974520, oid_value = 
22974520}, next = 0x15e9820}
(gdb) p *rtable->head->next->next->next->next
$15 = {data = {ptr_value = 0x15e9840, int_value = 22976576, oid_value = 
22976576}, next = 0x15e7998}
===========================

The line which starts with "$15" has 0x15e7998 as its next data.
But it is the head pointer(see the line which starts with $10).

And in range_table_walker(), the function is called recursively.
--------
...
         if (!(flags & QTW_IGNORE_RANGE_TABLE))
         {
                 if (range_table_walker(query->rtable, walker, context, 
flags))
                         return true;
         }
...
--------

We should make rtable right or deal with "flags" properly.
But I can't find where to do it...

What do you think ?

regards,
---------
NTT Software Corporation
Tomonari Katsumata