Re: [Maria-developers] MDEV-4978 - Server cursor is broken with blobs in the select list

6 Sep 2013

Hi Sergei,

06.09.2013, в 15:29, Sergei Golubchik  написал(а):
...
Hi, Sergey!
On Sep 06, Sergey Vojtovich wrote:
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revno: 3878
revision-id: svoj@mariadb.org-20130906111656-oy2c3pwy2o1q0zqn
parent: wlad@montyprogram.com-20130903204512-hgwu77prle0lw7a3
committer: Sergey Vojtovich 
branch nick: 5.5-mdev4978
timestamp: Fri 2013-09-06 15:16:56 +0400
message:
 MDEV-4978 - Server cursor is broken with blobs in the select list,
             ORDER BY does not work
Use "dynamic" row format (instead of "block") for MARIA internal
 temporary tables created for cursors.
 With "block" row format MARIA may shuffle rows, with "dynamic" row
 format records are inserted sequentially (there are no gaps in data
 file while we fill temporary tables).
 This is needed to preserve row order when scanning materialized cursors.
...
=== modified file 'sql/sql_select.cc'

--- a/sql/sql_select.cc	2013-09-03 14:41:07 +0000
+++ b/sql/sql_select.cc	2013-09-06 11:16:56 +0000
@@ -15373,7 +15374,8 @@ create_tmp_table(THD *thd, TMP_TABLE_PAR
  if (thd->is_fatal_error)				// If end of memory
    goto err;					 /* purecov: inspected */
  share->db_record_offset= 1;
-  table->used_for_duplicate_elimination= (param->sum_func_count == 0 &&
+  table->used_for_duplicate_elimination= keep_row_order ||
+                                         (param->sum_func_count == 0 &&
                                          (table->group || table->distinct));
That's very confusing. Why keep_row_order means that the table is "used
for duplicate elimination"?
I had to check the code to see that used_for_duplicate_elimination
affects the row format in Aria. This is not obvious too.
And it forces the row format to be DYNAMIC for a very different reason,
not for preserving row order.
Can't disagree.
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Perhaps it'd be better to rename used_for_duplicate_elimination to
"force_dynamic_Aria_row_format" ? A prettier solution would be to
introduce another flag: table->keep_row_order.
I submitted another patch with the "prettier" solution. Though I tend to think that it'd
be better not to fill TABLE object with things like keep_row_order and
used_for_duplicate_elimination - they can go as an argument to
create_internal_tmp_table(force_dynamic_aria_row_format).

Thanks,
Sergey
...
Regards,
Sergei


    