maria-developers team mailing list archive

[Sergey Petrunia <sergey@xxxxxxxxxxx>]

Hi Varun,


On Thu, May 24, 2018 at 03:17:02AM +0530, Varun wrote:
> revision-id: de722585c1b2ad2af99bd1749e8566ea77838764 (mariadb-5.5.56-219-gde722585c1b)
> parent(s): 1ada4afb0a51f7283b6187a95019ec2cb80c8a0b
> author: Varun Gupta
> committer: Varun Gupta
> timestamp: 2018-05-24 03:09:42 +0530
> message:
> 
> MDEV-16225: wrong resultset from query with semijoin=on
> 
> For non-semi-join subquery optimization we do a cost based decision between
> Materialisation and IN -> EXIST transformation. The issue in this case is that for IN->EXIST transformation
> we run JOIN::reoptimize with the IN->EXISt conditions and we come up with a new query plan. But when we compare
> the cost with Materialization, we make the decision to chose Materialization so we need to restore the query plan
> for Materilization. The restoring of query plan is not handled correctly.
> 
> diff --git a/sql/sql_select.cc b/sql/sql_select.cc
> index d6d269a700f..b8d43b9797e 100644
> --- a/sql/sql_select.cc
> +++ b/sql/sql_select.cc
> @@ -23805,6 +23805,22 @@ void JOIN::restore_query_plan(Join_plan_state *restore_from)
>      }
>  
>    }
> +  else
> +  {
> +    /*
> +      After running JOIN::reoptimize for IN->EXISTS
> +      transformation we might add elements to the keyuse array,
> +      The original query plan was that the keyuse array had no elements, so we
> +      should restore that state here.
> +    */
> +    while(keyuse.elements)
> +      delete_dynamic_element(&keyuse, 0);

I'm wondering, why do we need the above loop and not just delete everything
with delete_dynamic().

But if I don't miss anything, this is not significant.
Ok to push either the above variant or one with delete_dynamic().

> +    for (uint i= 0; i < table_count; i++)
> +    {
> +      join_tab[i].keyuse= NULL;
> +      join_tab[i].checked_keys.clear_all();
> +    }
> +  }
>    memcpy((uchar*) best_positions, (uchar*) restore_from->best_positions,
>           sizeof(POSITION) * (table_count + 1));
>    /* Restore SJM nests */
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-- 
BR
 Sergei
-- 
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog