MDEV-29129: Performance regression starting in 10.6: select order by …

…limit ...

The cause of regression was handling for ROWNUM() function.
For queries like

  SELECT ROWNUM() FROM ... ORDER BY ...

ROWNUM() should be computed before the ORDER BY.
The computation was moved to be before the ORDER BY for any entries in
the select list that had RAND_TABLE_BIT set.

This had a negative impact on queries in form:

  SELECT sp_func() FROM t1 ORDER BY ... LIMIT n

where sp_func() is NOT declared as DETERMINISTIC (and so has
RAND_TABLE_BIT set).

The fix is to require evaluation for sorting only for the ROWNUM()
function. Functions that just have RAND_TABLE_BIT() can be computed
after ORDER BY ... LIMIT is applied.

(think about a possible index that satisfies the ORDER BY clause. In
that case, the the rows would be read in the needed order and we would
stop after reading LIMIT rows, achieving the same effect).

mysql-test/main/derived_view.result

@@ -2696,7 +2696,7 @@ ON p.id = g.p_random
 ORDER BY gallery_name ASC 
 ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	10	Using temporary; Using filesort
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	10	Using filesort
 1	PRIMARY	p	eq_ref	PRIMARY	PRIMARY	4	g.p_random	1	Using where
 2	DERIVED	gal	ALL	NULL	NULL	NULL	NULL	10	
 3	DEPENDENT SUBQUERY	pi	ref	gallery_id	gallery_id	4	test.gal.id	4	Using temporary; Using filesort

mysql-test/main/having.result

@@ -834,13 +834,13 @@ test.t1	analyze	status	Engine-independent statistics collected
 test.t1	analyze	status	OK
 explain SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t) GROUP BY t HAVING r = 1  ORDER BY t1.u;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	8	Using temporary; Using filesort
+1	SIMPLE	t1	index	NULL	t	5	NULL	8	Using temporary; Using filesort
 SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t) GROUP BY t HAVING r = 1  ORDER BY t1.u;
 t	r
 10	1
 12	1
-14	1
-16	1
+15	1
+17	1
 DROP TABLE t1;
 DROP FUNCTION next_seq_value;
 DROP TABLE series;

mysql-test/main/show_explain.result

@@ -1007,7 +1007,7 @@ SELECT a+SLEEP(0.01) FROM t1
 WHERE a IN ( 255, 0 ) OR b BETWEEN 6 AND 129
 ORDER BY b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	8	Using sort_union(a,b); Using where; Using temporary; Using filesort
+1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	8	Using sort_union(a,b); Using where; Using filesort
 set @show_explain_probe_select_id=1;
 SET debug_dbug='+d,show_explain_probe_join_exec_start';
 SELECT a+SLEEP(0.01) FROM t1
@@ -1016,7 +1016,7 @@ ORDER BY b;
 connection default;
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	8	Using sort_union(a,b); Using where; Using temporary; Using filesort
+1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	8	Using sort_union(a,b); Using where; Using filesort
 Warnings:
 Note	1003	SELECT a+SLEEP(0.01) FROM t1
 WHERE a IN ( 255, 0 ) OR b BETWEEN 6 AND 129
@@ -1039,7 +1039,7 @@ ORDER BY b;
 connection default;
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	8	Using sort_union(a,b); Using where; Using temporary; Using filesort
+1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	8	Using sort_union(a,b); Using where; Using filesort
 Warnings:
 Note	1003	SELECT a+SLEEP(0.01) FROM t1
 WHERE a IN ( 255, 0 ) OR b BETWEEN 6 AND 129

mysql-test/main/sp.result

@@ -8932,3 +8932,43 @@ ERROR 42000: PROCEDURE does not support subqueries or stored functions
 DROP TABLE t1;
 # End of 10.4 tests
 #
+#
+# MDEV-29129: Performance regression starting in 10.6: unlimited "select order by limit"
+#
+CREATE TABLE t1 (
+lookupId int primary key,
+value varchar(255)
+);
+insert into t1 select seq, seq from seq_1_to_100;
+# Note: the function is intentionally NOT declared as DETERMINISTIC
+CREATE FUNCTION f1(LOOKUPID_IN INT) RETURNS varchar(255) CHARSET utf8
+BEGIN
+DECLARE LOOKUP_VALUE VARCHAR(255);
+SET LOOKUP_VALUE = (SELECT value FROM t1 WHERE lookupId = LOOKUPID_IN);
+set @counter=@counter+1;
+RETURN LOOKUP_VALUE;
+END; 
+//
+create table t2 (
+col1 int,
+col2 int
+);
+insert into t2 select mod(seq,100), seq from seq_1_to_1000;
+explain 
+select f1(col1) from t2 order by col2 desc limit 5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	1000	Using filesort
+set @counter=0;
+select f1(col1) from t2 order by col2 desc limit 5;
+f1(col1)
+NULL
+99
+98
+97
+96
+# Must show 5, not 1000:
+select @counter;
+@counter
+5
+drop function f1;
+drop table t1,t2;

mysql-test/main/sp.test

@@ -10519,3 +10519,40 @@ DROP TABLE t1;
 
 --echo # End of 10.4 tests
 --echo #
+
+--echo #
+--echo # MDEV-29129: Performance regression starting in 10.6: unlimited "select order by limit"
+--echo #
+
+CREATE TABLE t1 (
+  lookupId int primary key,
+  value varchar(255)
+);
+insert into t1 select seq, seq from seq_1_to_100;
+
+-- echo # Note: the function is intentionally NOT declared as DETERMINISTIC
+delimiter //;
+CREATE FUNCTION f1(LOOKUPID_IN INT) RETURNS varchar(255) CHARSET utf8
+BEGIN
+  DECLARE LOOKUP_VALUE VARCHAR(255);
+  SET LOOKUP_VALUE = (SELECT value FROM t1 WHERE lookupId = LOOKUPID_IN);
+  set @counter=@counter+1;
+  RETURN LOOKUP_VALUE;
+END; 
+//
+delimiter ;//
+
+create table t2 (
+  col1 int,
+  col2 int
+);
+insert into t2 select mod(seq,100), seq from seq_1_to_1000;
+
+explain 
+select f1(col1) from t2 order by col2 desc limit 5;
+set @counter=0;
+select f1(col1) from t2 order by col2 desc limit 5;
+--echo # Must show 5, not 1000:
+select @counter;
+drop function f1;
+drop table t1,t2;

mysql-test/main/user_var.result

@@ -372,14 +372,14 @@ insert into t1 (b) values (10), (30), (10), (10);
 set @var := 0;
 explain select if(b=@var, 999, b) , @var := b from t1  order by b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using filesort
 set @var := 0;
 select if(b=@var, 999, b) , @var := b from t1  order by b;
 if(b=@var, 999, b)	@var := b
 10	10
-10	10
 30	30
 999	10
+999	10
 drop table t1;
 create temporary table t1 (id int);
 insert into t1 values (2), (3), (3), (4);

sql/sql_base.cc

@@ -7738,6 +7738,8 @@ bool setup_fields(THD *thd, Ref_ptr_array ref_pointer_array,
     thd->lex->current_select->select_list_tables|= item->used_tables();
     thd->lex->used_tables|= item->used_tables();
     thd->lex->current_select->cur_pos_in_select_list++;
+
+    thd->lex->current_select->rownum_in_field_list |= item->with_rownum_func();
   }
   thd->lex->current_select->is_item_list_lookup= save_is_item_list_lookup;
   thd->lex->current_select->cur_pos_in_select_list= UNDEF_POS;

sql/sql_lex.cc

@@ -3002,6 +3002,8 @@ void st_select_lex::init_query()
   prep_leaf_list_state= UNINIT;
   bzero((char*) expr_cache_may_be_used, sizeof(expr_cache_may_be_used));
   select_list_tables= 0;
+  rownum_in_field_list= 0;
+
   window_specs.empty();
   window_funcs.empty();
   tvc= 0;

sql/sql_lex.h

@@ -1344,6 +1344,9 @@ class st_select_lex: public st_select_lex_node
   */
   table_map select_list_tables;
 
+  /* Set to 1 if any field in field list has ROWNUM() */
+  bool rownum_in_field_list;
+
   /* namp of nesting SELECT visibility (for aggregate functions check) */
   nesting_map name_visibility_map;
   table_map with_dep;

sql/sql_select.cc

@@ -434,7 +434,6 @@ void JOIN::init(THD *thd_arg, List<Item> &fields_arg,
   no_order= 0;
   simple_order= 0;
   simple_group= 0;
-  rand_table_in_field_list= 0;
   ordered_index_usage= ordered_index_void;
   need_distinct= 0;
   skip_sort_order= 0;
@@ -1434,7 +1433,6 @@ JOIN::prepare(TABLE_LIST *tables_init, COND *conds_init, uint og_num,
                    &all_fields, &select_lex->pre_fix, 1))
     DBUG_RETURN(-1);
   thd->lex->current_select->context_analysis_place= save_place;
-  rand_table_in_field_list= select_lex->select_list_tables & RAND_TABLE_BIT;
 
   if (setup_without_group(thd, ref_ptrs, tables_list,
                           select_lex->leaf_tables, fields_list,
@@ -14807,7 +14805,7 @@ remove_const(JOIN *join,ORDER *first_order, COND *cond,
     and some wrong results so better to leave the code as it was
     related to ROLLUP.
   */
-  *simple_order= !join->rand_table_in_field_list;
+  *simple_order= !join->select_lex->rownum_in_field_list;
   if (join->only_const_tables())
     return change_list ? 0 : first_order;		// No need to sort
 

sql/sql_select.h

@@ -1420,11 +1420,6 @@ class JOIN :public Sql_alloc
     GROUP/ORDER BY.
   */
   bool simple_order, simple_group;
-  /*
-    Set to 1 if any field in field list has RAND_TABLE set. For example if
-    if one uses RAND() or ROWNUM() in field list
-  */
-  bool rand_table_in_field_list;
 
   /*
     ordered_index_usage is set if an ordered index access