mariadb-columnstore-engine/dbcon/mysql/ha_mcs_opt_rewrites.cpp

/* Copyright (C) 2019-20 MariaDB Corporation

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; version 2 of
   the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA. */

#include <typeinfo>

#include "ha_mcs_opt_rewrites.h"

/*@brief  in_subselect_rewrite_walk - Rewrites Item_in_subselect*/
/************************************************************
* DESCRIPTION:
* It traverses filter predicates searching for
* Item_in_subselect and rewrites it adding equi-join predicate
* to finalise IN_2_EXISTS rewrite.
* PARAMETERS:
*    item_arg - Item to check.
*    arg - bool to early return if predicate injection fails.
* RETURN:
***********************************************************/
void in_subselect_rewrite_walk(const Item* item_arg, void* arg)
{
    bool* result= reinterpret_cast<bool*>(arg);
    if (*result) return;

    Item* item= const_cast<Item*>(item_arg);

    JOIN* join= nullptr;
    if (typeid(*item) == typeid(Item_in_subselect))
    {
        Item_in_subselect* sub= reinterpret_cast<Item_in_subselect*>(item);
        // MCS 1.4.3 doesn't support IN + subquery with UNION so
        // we safe to take this JOIN.
        join= sub->unit->first_select()->join;
        // Inject equi-JOIN predicates if needed.
        *result= sub->create_in_to_exists_cond(join);
        *result= (*result) ? *result :
            sub->inject_in_to_exists_cond(join);
        sub->unit->first_select()->prep_where=
            join->conds ? join->conds->copy_andor_structure(current_thd) : 0;
    }
    else if (typeid(*item) == typeid(Item_singlerow_subselect))
    {
        Item_singlerow_subselect* sub=
            reinterpret_cast<Item_singlerow_subselect*>(item);
        // MCS 1.4.3 doesn't support IN + subquery with UNION so
        // we safe to take this JOIN.
        join= sub->unit->first_select()->join;
    }
    else
    {
        // Exit for any but dedicated Items.
        return;
    }

    // Walk recursively to process nested IN ops.
    if (join->conds)
    {
        join->conds->traverse_cond(in_subselect_rewrite_walk,
            arg, Item::POSTFIX);
    }
}

// Sets SELECT_LEX::first_cond_optimization
void first_cond_optimization_flag_set(SELECT_LEX* select_lex)
{
    select_lex->first_cond_optimization = true;
}

// Unsets SELECT_LEX::first_cond_optimization
void first_cond_optimization_flag_unset(SELECT_LEX* select_lex)
{
    select_lex->first_cond_optimization = false;
}

/* @brief  first_cond_optimization_flag_toggle() - Sets/Unsets first_cond_optimization */
/************************************************************
* DESCRIPTION:
* This function traverses SELECT_LEX::table_list recursively
* to set/unset SELECT_LEX::first_cond_optimization: a marker
* to control optimizations executing PS. If set it allows to
* apply optimizations. If unset, it disables optimizations.
* PARAMETERS:
*    select_lex - SELECT_LEX* that describes the query.
*    func - Pointer to a function which either sets/unsets
*           SELECT_LEX::first_cond_optimization
***********************************************************/
void first_cond_optimization_flag_toggle(SELECT_LEX *select_lex, void (*func)(SELECT_LEX*))
{
    for (TABLE_LIST *tl= select_lex->get_table_list(); tl; tl= tl->next_local)
    {
        if (tl->is_view_or_derived())
        {
            SELECT_LEX_UNIT *unit= tl->get_unit();

            if (unit)
            {
                for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
                {
                    first_cond_optimization_flag_toggle(sl, func);
                }
            }
        }
    }

    (*func)(select_lex);
}


/* @brief  in_subselect_rewrite - Rewrites Item_in_subselect */
/************************************************************
* DESCRIPTION:
* This function traverses TABLE_LISTs running in_subselect_rewrite_walk
* PARAMETERS:
*    select_lex - SELECT_LEX* that describes the query.
* RETURN:
*    bool to indicate predicate injection failures.
***********************************************************/
bool in_subselect_rewrite(SELECT_LEX *select_lex)
{
    bool result = false;
    TABLE_LIST *tbl;
    List_iterator_fast<TABLE_LIST> li(select_lex->leaf_tables);

    while (!result && (tbl = li++))
    {
        if (tbl->is_view_or_derived())
        {
            SELECT_LEX_UNIT *unit= tbl->get_unit();

            for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
                result = in_subselect_rewrite(sl);
        }
    }

    if (select_lex->join && select_lex->join->conds)
    {
        select_lex->join->conds->traverse_cond(in_subselect_rewrite_walk, &result,
            Item::POSTFIX);
    }

    return result;
}