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MDEV-4029 SELECT on information_schema using a subquery locks up the information_schema table due to incorrect mutexes handling

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Early evaluation of subqueries in the WHERE conditions on I_S.*_STATUS tables,
otherwise the subquery on this same table will try to acquire LOCK_status twice.
This commit is contained in:
Sergei Golubchik 2013-01-21 10:52:39 +01:00
parent 2e11ca36f2
commit 43c6953fa1
3 changed files with 29 additions and 6 deletions
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8
mysql-test/r/information_schema2.result Normal file
View File

@ -0,0 +1,8 @@
select variable_name from information_schema.session_status where variable_name =
(select variable_name from information_schema.session_status where variable_name = 'uptime');
variable_name
UPTIME
select variable_name from information_schema.session_variables where variable_name =
(select variable_name from information_schema.session_variables where variable_name = 'basedir');
variable_name
BASEDIR

9
mysql-test/t/information_schema2.test Normal file
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@ -0,0 +1,9 @@
#
# MDEV-4029 SELECT on information_schema using a subquery locks up the information_schema table due to incorrect mutexes handling
#
select variable_name from information_schema.session_status where variable_name =
(select variable_name from information_schema.session_status where variable_name = 'uptime');
select variable_name from information_schema.session_variables where variable_name =
(select variable_name from information_schema.session_variables where variable_name = 'basedir');

18
sql/sql_show.cc
View File

@ -2260,7 +2260,6 @@ static bool show_status_array(THD *thd, const char *wild,
int len; int len;
LEX_STRING null_lex_str; LEX_STRING null_lex_str;
SHOW_VAR tmp, *var; SHOW_VAR tmp, *var;
COND *partial_cond= 0;
enum_check_fields save_count_cuted_fields= thd->count_cuted_fields; enum_check_fields save_count_cuted_fields= thd->count_cuted_fields;
bool res= FALSE; bool res= FALSE;
CHARSET_INFO *charset= system_charset_info; CHARSET_INFO *charset= system_charset_info;
@ -2274,7 +2273,6 @@ static bool show_status_array(THD *thd, const char *wild,
if (*prefix) if (*prefix)
*prefix_end++= '_'; *prefix_end++= '_';
len=name_buffer + sizeof(name_buffer) - prefix_end; len=name_buffer + sizeof(name_buffer) - prefix_end;
partial_cond= make_cond_for_info_schema(cond, table->pos_in_table_list);
for (; variables->name; variables++) for (; variables->name; variables++)
{ {
@ -2297,13 +2295,13 @@ static bool show_status_array(THD *thd, const char *wild,
if (show_type == SHOW_ARRAY) if (show_type == SHOW_ARRAY)
{ {
show_status_array(thd, wild, (SHOW_VAR *) var->value, value_type, show_status_array(thd, wild, (SHOW_VAR *) var->value, value_type,
status_var, name_buffer, table, ucase_names, partial_cond); status_var, name_buffer, table, ucase_names, cond);
} }
else else
{ {
if (!(wild && wild[0] && wild_case_compare(system_charset_info, if (!(wild && wild[0] && wild_case_compare(system_charset_info,
name_buffer, wild)) && name_buffer, wild)) &&
(!partial_cond || partial_cond->val_int())) (!cond || cond->val_int()))
{ {
char *value=var->value; char *value=var->value;
const char *pos, *end; // We assign a lot of const's const char *pos, *end; // We assign a lot of const's
@ -5562,9 +5560,12 @@ int fill_variables(THD *thd, TABLE_LIST *tables, COND *cond)
schema_table_idx == SCH_GLOBAL_VARIABLES) schema_table_idx == SCH_GLOBAL_VARIABLES)
option_type= OPT_GLOBAL; option_type= OPT_GLOBAL;
COND *partial_cond= make_cond_for_info_schema(cond, tables);
rw_rdlock(&LOCK_system_variables_hash); rw_rdlock(&LOCK_system_variables_hash);
res= show_status_array(thd, wild, enumerate_sys_vars(thd, sorted_vars), res= show_status_array(thd, wild, enumerate_sys_vars(thd, sorted_vars),
option_type, NULL, "", tables->table, upper_case_names, cond); option_type, NULL, "", tables->table, upper_case_names,
partial_cond);
rw_unlock(&LOCK_system_variables_hash); rw_unlock(&LOCK_system_variables_hash);
DBUG_RETURN(res); DBUG_RETURN(res);
} }
@ -5601,13 +5602,18 @@ int fill_status(THD *thd, TABLE_LIST *tables, COND *cond)
tmp1= &thd->status_var; tmp1= &thd->status_var;
} }
COND *partial_cond= make_cond_for_info_schema(cond, tables);
// Evaluate and cache const subqueries now, before the mutex.
if (partial_cond)
partial_cond->val_int();
pthread_mutex_lock(&LOCK_status); pthread_mutex_lock(&LOCK_status);
if (option_type == OPT_GLOBAL) if (option_type == OPT_GLOBAL)
calc_sum_of_all_status(&tmp); calc_sum_of_all_status(&tmp);
res= show_status_array(thd, wild, res= show_status_array(thd, wild,
(SHOW_VAR *)all_status_vars.buffer, (SHOW_VAR *)all_status_vars.buffer,
option_type, tmp1, "", tables->table, option_type, tmp1, "", tables->table,
upper_case_names, cond); upper_case_names, partial_cond);
pthread_mutex_unlock(&LOCK_status); pthread_mutex_unlock(&LOCK_status);
DBUG_RETURN(res); DBUG_RETURN(res);
} }