MDEV-299: SHOW EXPLAIN: Plan produced by SHOW EXPLAIN changes back and forth during query execution

- Make SHOW EXPLAIN ignore range accesses when printing "Range checked for each record" plans.

mysql-test/r/show_explain.result

@@ -550,4 +550,50 @@ test
 test
 set debug_dbug='';
 DROP TABLE t1;
+#
+# MDEV-299: SHOW EXPLAIN: Plan produced by SHOW EXPLAIN changes back and forth during query execution
+#
+create table t1 (key1 int, col1 int, col2 int, filler char(100), key(key1));
+insert into t1 select A.a+ 10 * B.a, 10, 10, 'filler-data' from t0 A, t0 B;
+update t1 set col1=3, col2=10 where key1=1;
+update t1 set col1=3, col2=1000 where key1=2;
+update t1 set col1=3, col2=10 where key1=3;
+update t1 set col1=3, col2=1000 where key1=4;
+set @tmp_mdev299_jcl= @@join_cache_level;
+set join_cache_level=0;
+explain select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	A	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	B	ALL	key1	NULL	NULL	NULL	100	Range checked for each record (index map: 0x1)
+set @show_explain_probe_select_id=1;
+set debug_dbug='d,show_explain_probe_test_if_quick_select';
+select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100;
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	A	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	B	ALL	key1	NULL	NULL	NULL	100	Range checked for each record (index map: 0x1)
+Warnings:
+Note	1003	select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	A	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	B	ALL	key1	NULL	NULL	NULL	100	Range checked for each record (index map: 0x1)
+Warnings:
+Note	1003	select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	A	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	B	ALL	key1	NULL	NULL	NULL	100	Range checked for each record (index map: 0x1)
+Warnings:
+Note	1003	select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	A	ALL	NULL	NULL	NULL	NULL	100	Using where
+1	SIMPLE	B	ALL	key1	NULL	NULL	NULL	100	Range checked for each record (index map: 0x1)
+Warnings:
+Note	1003	select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100
+count(*)
+212
+set debug_dbug='';
+drop table t1;
 drop table t0;

mysql-test/t/show_explain.test

@@ -542,6 +542,44 @@ set debug_dbug='';
 DROP TABLE t1;
 
 
+--echo #
+--echo # MDEV-299: SHOW EXPLAIN: Plan produced by SHOW EXPLAIN changes back and forth during query execution
+--echo #
+
+create table t1 (key1 int, col1 int, col2 int, filler char(100), key(key1));
+insert into t1 select A.a+ 10 * B.a, 10, 10, 'filler-data' from t0 A, t0 B;
+
+# Make matches 3 records 
+update t1 set col1=3, col2=10 where key1=1; # small range
+update t1 set col1=3, col2=1000 where key1=2; # big range 
+update t1 set col1=3, col2=10 where key1=3; # small range again
+update t1 set col1=3, col2=1000 where key1=4; # big range 
+
+set @tmp_mdev299_jcl= @@join_cache_level;
+set join_cache_level=0;
+
+explain select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100;
+
+set @show_explain_probe_select_id=1;
+set debug_dbug='d,show_explain_probe_test_if_quick_select';
+
+send 
+select count(*) from t1 A, t1 B where B.key1 < A.col2 and A.col1=3 AND B.col2 + 1 < 100;
+
+connection default;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+connection con1;
+reap;
+
+set debug_dbug='';
+drop table t1;
 
 
 ## TODO: Test this: have several SHOW EXPLAIN requests be queued up for a

sql/sql_select.cc

@@ -16912,6 +16912,14 @@ int read_first_record_seq(JOIN_TAB *tab)
 static int
 test_if_quick_select(JOIN_TAB *tab)
 {
+  DBUG_EXECUTE_IF("show_explain_probe_test_if_quick_select", 
+                  if (dbug_user_var_equals_int(tab->join->thd, 
+                                               "show_explain_probe_select_id", 
+                                               tab->join->select_lex->select_number))
+                        dbug_serve_apcs(tab->join->thd, 1);
+                 );
+
+
   delete tab->select->quick;
   tab->select->quick=0;
   return tab->select->test_quick_select(tab->join->thd, tab->keys,
@@ -21410,6 +21418,7 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
       tmp3.length(0);
       tmp4.length(0);
       quick_type= -1;
+      QUICK_SELECT_I *quick= NULL;
 
       /* Don't show eliminated tables */
       if (table->map & join->eliminated_tables)
@@ -21428,8 +21437,9 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
       
       enum join_type tab_type= tab->type;
       if ((tab->type == JT_ALL || tab->type == JT_HASH) &&
-           tab->select && tab->select->quick)
+           tab->select && tab->select->quick && tab->use_quick != 2)
       {
+        quick= tab->select->quick;
         quick_type= tab->select->quick->get_type();
         if ((quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE) ||
             (quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT) ||
@@ -21568,9 +21578,9 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
           tab->select && tab->select->quick)
 =======*/
       }         
-      if (tab->type != JT_CONST && tab->select && tab->select->quick)
+      if (tab->type != JT_CONST && tab->select && quick)
         tab->select->quick->add_keys_and_lengths(&tmp2, &tmp3);
-      if (key_info || (tab->select && tab->select->quick))
+      if (key_info || (tab->select && quick))
       {
         if (tmp2.length())
           item_list.push_back(new Item_string(tmp2.ptr(),tmp2.length(),cs));
@@ -21631,8 +21641,8 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
       else
       {
         ha_rows examined_rows;
-        if (tab->select && tab->select->quick)
-          examined_rows= tab->select->quick->records;
+        if (tab->select && quick)
+          examined_rows= quick->records;
         else if (tab_type == JT_NEXT || tab_type == JT_ALL || is_hj)
         {
           if (tab->limit)
@@ -21676,7 +21686,7 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
           table->covering_keys.is_set(tab->index))
 	key_read=1;
       if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT &&
-          !((QUICK_ROR_INTERSECT_SELECT*)tab->select->quick)->need_to_fetch_row)
+          !((QUICK_ROR_INTERSECT_SELECT*)quick)->need_to_fetch_row)
         key_read=1;
         
       if (tab->info)
@@ -21704,8 +21714,8 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
         uint keyno= MAX_KEY;
         if (tab->ref.key_parts)
           keyno= tab->ref.key;
-        else if (tab->select && tab->select->quick)
-          keyno = tab->select->quick->index;
+        else if (tab->select && quick)
+          keyno = quick->index;
 
         if (keyno != MAX_KEY && keyno == table->file->pushed_idx_cond_keyno &&
             table->file->pushed_idx_cond)