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cleanup: Select_limit_counters rename set_unlimited to clear

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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.
This commit is contained in:
Vicențiu Ciorbaru 2021-03-28 21:09:51 +03:00
parent 3fcc4f6fc2
commit 2d595319bf
4 changed files with 20 additions and 6 deletions
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2
sql/sql_lex.cc
View File

@ -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;

18
sql/sql_limit.h
View File

@ -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

4
sql/sql_parse.cc
View File

@ -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;

2
sql/sql_union.cc
View File

@ -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))
{