maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Sergey!

On Sep 06, Sergey Vojtovich wrote:
> revno: 3878
> revision-id: svoj@xxxxxxxxxxx-20130906111656-oy2c3pwy2o1q0zqn
> parent: wlad@xxxxxxxxxxxxxxxx-20130903204512-hgwu77prle0lw7a3
> committer: Sergey Vojtovich <svoj@xxxxxxxxxxx>
> 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.

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.

Regards,
Sergei