MDEV-36761 Remove @@new_mode=FIX_INDEX_STATS_FOR_ALL_NULLS in 12.1

Remove the FIX_INDEX_STATS_FOR_ALL_NULLS flag from @@new_mode.
The new behavior is now always on.

mysql-test/main/null_aware_cardinality.result

@@ -1,4 +1,3 @@
-SET @session_start_value = @@new_mode;
 # Small driving table
 CREATE TABLE t1 (a INT, b INT);
 INSERT INTO t1 VALUES (1, 1), (2, 2000),(3,300);
@@ -14,9 +13,6 @@ ANALYZE TABLE t2 PERSISTENT FOR ALL;
 Table	Op	Msg_type	Msg_text
 test.t2	analyze	status	Engine-independent statistics collected
 test.t2	analyze	status	Table is already up to date
-SET @@new_mode = "FIX_INDEX_STATS_FOR_ALL_NULLS";
-Warnings:
-Warning	4200	The setting 'new_mode=FIX_INDEX_STATS_FOR_ALL_NULLS' is ignored. It only exists for compatibility with old installations and will be removed in a future release
 # NULL-rejecting equality t1.b = t2.b will not return any matches
 # because all values of t2.b are NULL. So "rows" = 1 for t2 where 1 is
 # a special value meaning "very few" rows
@@ -82,23 +78,12 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t3	ref	key_ab	key_ab	10	test.t1.a,const	11	100.00	Using where; Using index
 Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t3`.`a` AS `a`,`test`.`t3`.`b` AS `b` from `test`.`t1` join `test`.`t3` where `test`.`t3`.`a` = `test`.`t1`.`a` and `test`.`t3`.`b` is null
-# In the old mode (null-aware estimation is not enabled), "rows" > 1
-SET @@new_mode = "";
-EXPLAIN EXTENDED SELECT * FROM t1 JOIN t2 ON t1.a = t2.a AND t1.b = t2.b;
-id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
-1	SIMPLE	t2	ref	key_b	key_b	5	test.t1.b	100	100.00	Using where
-Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t2` where `test`.`t2`.`a` = `test`.`t1`.`a` and `test`.`t2`.`b` = `test`.`t1`.`b`
 # Insert some non-NULL values and re-collect the stats
 INSERT INTO t3 SELECT 1, 1 FROM seq_1_to_100;
 ANALYZE TABLE t3 PERSISTENT FOR COLUMNS (b) INDEXES (key_ab);
 Table	Op	Msg_type	Msg_text
 test.t3	analyze	status	Engine-independent statistics collected
 test.t3	analyze	status	OK
-SET @@new_mode = "FIX_INDEX_STATS_FOR_ALL_NULLS";
-Warnings:
-Warning	4200	The setting 'new_mode=FIX_INDEX_STATS_FOR_ALL_NULLS' is ignored. It only exists for compatibility with old installations and will be removed in a future release
 EXPLAIN EXTENDED SELECT * FROM t1 JOIN t3 ON t1.a = t3.a AND t1.b = t3.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where
@@ -158,5 +143,4 @@ EXPLAIN SELECT * FROM t1, t2 WHERE t2.a=t1.a AND t2.b=t1.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	Using where
 1	SIMPLE	t2	ref	i1	i1	66	test.t1.a,test.t1.a	1	Using where
-SET @@new_mode = @session_start_value;
 DROP TABLE t1, t2;

mysql-test/main/null_aware_cardinality.test

@@ -1,7 +1,5 @@
 --source include/have_sequence.inc
 
-SET @session_start_value = @@new_mode;
-
 --echo # Small driving table
 CREATE TABLE t1 (a INT, b INT);
 INSERT INTO t1 VALUES (1, 1), (2, 2000),(3,300);
@@ -15,8 +13,6 @@ INSERT INTO t2 SELECT seq/100,  NULL FROM seq_1_to_1000;
 
 ANALYZE TABLE t2 PERSISTENT FOR ALL;
 
-SET @@new_mode = "FIX_INDEX_STATS_FOR_ALL_NULLS";
-
 --echo # NULL-rejecting equality t1.b = t2.b will not return any matches
 --echo # because all values of t2.b are NULL. So "rows" = 1 for t2 where 1 is
 --echo # a special value meaning "very few" rows
@@ -52,16 +48,11 @@ EXPLAIN EXTENDED SELECT * FROM t1 JOIN t3 ON t1.a = t3.a AND t1.b <=> t3.b;
 
 EXPLAIN EXTENDED SELECT * FROM t1 JOIN t3 ON t1.a = t3.a AND t3.b is NULL;
 
---echo # In the old mode (null-aware estimation is not enabled), "rows" > 1
-SET @@new_mode = "";
-EXPLAIN EXTENDED SELECT * FROM t1 JOIN t2 ON t1.a = t2.a AND t1.b = t2.b;
-
 --echo # Insert some non-NULL values and re-collect the stats
 INSERT INTO t3 SELECT 1, 1 FROM seq_1_to_100;
 
 ANALYZE TABLE t3 PERSISTENT FOR COLUMNS (b) INDEXES (key_ab);
 
-SET @@new_mode = "FIX_INDEX_STATS_FOR_ALL_NULLS";
 EXPLAIN EXTENDED SELECT * FROM t1 JOIN t3 ON t1.a = t3.a AND t1.b = t3.b;
 
 --echo # Test composite index for 3 columns. Key prefix is used for access
@@ -99,5 +90,4 @@ ANALYZE TABLE t2 PERSISTENT FOR COLUMNS (b) INDEXES (i1);
 
 EXPLAIN SELECT * FROM t1, t2 WHERE t2.a=t1.a AND t2.b=t1.a;
 
-SET @@new_mode = @session_start_value;
 DROP TABLE t1, t2;

sql/sql_statistics.cc

@@ -4164,11 +4164,10 @@ void set_statistics_for_table(THD *thd, TABLE *table)
         (check_eits_preferred(thd) &&
          table->stats_is_read &&
          key_info->read_stats->avg_frequency_is_inited() &&
-         key_info->read_stats->has_stats(thd));
+         key_info->read_stats->has_stats());
 
     // Fill out `all_nulls_key_parts` bitmap
-    if (TEST_NEW_MODE_FLAG(thd, NEW_MODE_FIX_INDEX_STATS_FOR_ALL_NULLS) &&
-        key_info->is_statistics_from_stat_tables)
+    if (key_info->is_statistics_from_stat_tables)
     {
       for (uint part_idx= 0; part_idx < key_info->usable_key_parts; part_idx++)
       {

sql/sql_statistics.h

@@ -614,13 +614,7 @@ public:
 
   void mark_stats_as_read() { stats_were_read= true; }
 
-  bool has_stats(THD *thd) const
-  {
-    if (TEST_NEW_MODE_FLAG(thd, NEW_MODE_FIX_INDEX_STATS_FOR_ALL_NULLS))
-      return stats_were_read;
-    else
-      return get_avg_frequency(0) > 0.5;
-  }
+  bool has_stats() const { return stats_were_read; }
 
   bool avg_frequency_is_inited() { return avg_frequency != NULL; }
 

sql/sys_vars.cc

@@ -4174,9 +4174,9 @@ static Sys_var_set Sys_old_behavior(
 */
 static const char *new_mode_all_names[]=
 {
-  "FIX_DISK_TMPTABLE_COSTS",
+  "FIX_DISK_TMPTABLE_COSTS",        // Default from here, See NEW_MODE_MAX
   "FIX_INDEX_STATS_FOR_ALL_NULLS",
-  "TEST_WARNING1",                       // Default from here, See NEW_MODE_MAX
+  "TEST_WARNING1",
   "TEST_WARNING2",
   0
 };