From 2d595319bf542dcdeeb058139efa2ef54f645c7b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Vicen=C8=9Biu=20Ciorbaru?= Date: Sun, 28 Mar 2021 21:09:51 +0300 Subject: cleanup: Select_limit_counters rename set_unlimited to clear The function was originally introduced by eb0804ef5e7eeb059bb193c3c6787e8a4188d34d MDEV-18553: MDEV-16327 pre-requisits part 1: isolation of LIMIT/OFFSET handling set_unlimited had an overloaded notion of both clearing the offset value and the limit value. The code is used for SQL_CALC_ROWS option to disable the limit clause after the limit is reached, while at the same time the calling code suppreses sending of rows. Proposed solution: Dedicated clear method for query initialization (to ensure no garbage remains between executions). Dedicated set_unlimited that only alters the limit value. --- sql/sql_lex.cc | 2 +- sql/sql_limit.h | 18 ++++++++++++++++-- sql/sql_parse.cc | 4 ++-- sql/sql_union.cc | 2 +- 4 files changed, 20 insertions(+), 6 deletions(-) diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc index ca7732316c7..69eaf5e174b 100644 --- a/sql/sql_lex.cc +++ b/sql/sql_lex.cc @@ -2910,7 +2910,7 @@ void st_select_lex_unit::init_query() { init_query_common(); set_linkage(GLOBAL_OPTIONS_TYPE); - lim.set_unlimited(); + lim.clear(); union_distinct= 0; prepared= optimized= optimized_2= executed= 0; bag_set_op_optimized= 0; diff --git a/sql/sql_limit.h b/sql/sql_limit.h index 6f32e5d17e9..60034201a50 100644 --- a/sql/sql_limit.h +++ b/sql/sql_limit.h @@ -37,8 +37,13 @@ class Select_limit_counters { offset_limit_cnt= offset; select_limit_cnt= limit; - if (select_limit_cnt + offset_limit_cnt >= - select_limit_cnt) + /* + Guard against an overflow condition, where limit + offset exceede + ha_rows value range. This case covers unreasonably large parameter + values that do not have any practical use so assuming in this case + that the query does not have a limit is fine. + */ + if (select_limit_cnt + offset_limit_cnt >= select_limit_cnt) select_limit_cnt+= offset_limit_cnt; else select_limit_cnt= HA_POS_ERROR; @@ -52,7 +57,16 @@ class Select_limit_counters bool is_unlimited() const { return select_limit_cnt == HA_POS_ERROR; } + /* + Set the limit to allow returning an unlimited number of rows. Useful + for cases when we want to continue execution indefinitely after the limit + is reached (for example for SQL_CALC_ROWS extension). + */ void set_unlimited() + { select_limit_cnt= HA_POS_ERROR; } + + /* Reset the limit entirely. */ + void clear() { select_limit_cnt= HA_POS_ERROR; offset_limit_cnt= 0; } bool check_offset(ha_rows sent) const diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc index 7f1045b7680..345bd50918c 100644 --- a/sql/sql_parse.cc +++ b/sql/sql_parse.cc @@ -7761,8 +7761,8 @@ void mysql_init_multi_delete(LEX *lex) { lex->sql_command= SQLCOM_DELETE_MULTI; mysql_init_select(lex); - lex->first_select_lex()->limit_params.select_limit= 0; - lex->unit.lim.set_unlimited(); + lex->first_select_lex()->limit_params.clear(); + lex->unit.lim.clear(); lex->first_select_lex()->table_list. save_and_clear(&lex->auxiliary_table_list); lex->query_tables= 0; diff --git a/sql/sql_union.cc b/sql/sql_union.cc index f1b00d75de4..2049dfe3ea1 100644 --- a/sql/sql_union.cc +++ b/sql/sql_union.cc @@ -1340,7 +1340,7 @@ bool st_select_lex_unit::prepare(TABLE_LIST *derived_arg, else { sl->join->result= result; - lim.set_unlimited(); + lim.clear(); if (!sl->join->procedure && result->prepare(sl->join->fields_list, this)) { -- cgit v1.2.1