Commit 973fb996 authored by Sergey Glukhov's avatar Sergey Glukhov
Browse files

Bug#38918 selecting from information_schema.columns is disproportionately slow 

The problem: table_open_method is not calculated properly if '*' is used in 'select'
The fix: added table_open_method calculation for such case
parent 8c6ffe36

mysql-test/r/information_schema.result

+9 −0
Original line number Diff line number Diff line
@@ -1646,4 +1646,13 @@ drop table t1; 
drop function f1;

select * from information_schema.tables where 1=sleep(100000);

select * from information_schema.columns where 1=sleep(100000);

explain select count(*) from information_schema.tables;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	tables	ALL	NULL	NULL	NULL	NULL	NULL	Skip_open_table; Scanned all databases

explain select count(*) from information_schema.columns;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	columns	ALL	NULL	NULL	NULL	NULL	NULL	Open_frm_only; Scanned all databases

explain select count(*) from information_schema.views;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	SIMPLE	views	ALL	NULL	NULL	NULL	NULL	NULL	Open_frm_only; Scanned all databases

End of 5.1 tests.

mysql-test/t/information_schema.test

+8 −0
Original line number Diff line number Diff line
@@ -1338,4 +1338,12 @@ where state='User sleep' and 
info='select * from information_schema.columns where 1=sleep(100000)';

--source include/wait_condition.inc





#

# Bug#38918 selecting from information_schema.columns is disproportionately slow

#

explain select count(*) from information_schema.tables;

explain select count(*) from information_schema.columns;

explain select count(*) from information_schema.views;



--echo End of 5.1 tests.

sql/sql_show.cc

+11 −1
Original line number Diff line number Diff line
@@ -2962,7 +2962,7 @@ static int fill_schema_table_names(THD *thd, TABLE *table, 
    @retval       SKIP_OPEN_TABLE | OPEN_FRM_ONLY | OPEN_FULL_TABLE

*/



static uint get_table_open_method(TABLE_LIST *tables,

uint get_table_open_method(TABLE_LIST *tables,

                                  ST_SCHEMA_TABLE *schema_table,

                                  enum enum_schema_tables schema_table_idx)

{
@@ -2973,12 +2973,22 @@ static uint get_table_open_method(TABLE_LIST *tables, 
  {

    Field **ptr, *field;

    int table_open_method= 0, field_indx= 0;

    uint star_table_open_method= OPEN_FULL_TABLE;

    bool used_star= true;                  // true if '*' is used in select

    for (ptr=tables->table->field; (field= *ptr) ; ptr++)

    {

      star_table_open_method=

        min(star_table_open_method,

            schema_table->fields_info[field_indx].open_method);

      if (bitmap_is_set(tables->table->read_set, field->field_index))

      {

        used_star= false;

        table_open_method|= schema_table->fields_info[field_indx].open_method;

      }

      field_indx++;

    }

    if (used_star)

      return star_table_open_method;

    return table_open_method;

  }

  /* I_S tables which use get_all_tables but can not be optimized */