MDEV-17024 Crash on large query

This problem manifested itself when a join query used two or more
materialized CTE such that each of them employed the same recursive CTE.
The bug caused a crash. The crash happened because the cleanup()
function was performed premature for recursive CTE. This clean up was
induced by the cleanup of the first CTE referenced the recusrsive CTE.
This cleanup destroyed the structures that would allow to read from the
temporary table containing the rows of the recursive CTE and an attempt to read
these rows for the second CTE referencing the recursive CTE triggered a
crash.
The clean up for a recursive CTE R should be performed after the cleanup
of the last materialized CTE that uses R.

mysql-test/r/cte_recursive.result

@@ -3300,3 +3300,96 @@ SELECT func();
 func()
 1
 DROP FUNCTION func;
+#
+# MDEV-17024: two materialized CTEs using the same recursive CTE
+#
+create table t1 (id int);
+insert into t1 values (1), (2), (3);
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2;
+c1	c2
+2	1
+explain extended with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<derived4>	ALL	NULL	NULL	NULL	NULL	6	100.00	
+1	PRIMARY	<derived5>	ALL	NULL	NULL	NULL	NULL	6	100.00	Using join buffer (flat, BNL join)
+4	DERIVED	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+4	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using join buffer (flat, BNL join)
+5	DERIVED	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+5	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using join buffer (flat, BNL join)
+2	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	RECURSIVE UNION	<derived2>	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	NULL	
+Warnings:
+Note	1003	with recursive rcte as (select 1 AS `a` union select cast(`rcte`.`a` + 1 as unsigned) AS `cast(a+1 as unsigned)` from `rcte` where `rcte`.`a` < 10), cte1 as (select count(0) AS `c1` from `rcte` join `test`.`t1` where `rcte`.`a` between 3 and 5 and `test`.`t1`.`id` = `rcte`.`a` - 3), cte2 as (select count(0) AS `c2` from `rcte` join `test`.`t1` where `rcte`.`a` between 7 and 8 and `test`.`t1`.`id` = `rcte`.`a` - 7)select `cte1`.`c1` AS `c1`,`cte2`.`c2` AS `c2` from `cte1` join `cte2`
+prepare stmt from "with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2";
+execute stmt;
+c1	c2
+2	1
+execute stmt;
+c1	c2
+2	1
+create table t2 (c1 int, c2 int);
+create procedure p() insert into t2 with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2;
+call p();
+select * from t2;
+c1	c2
+2	1
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1;
+c1
+2
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from t1),
+cte2 as
+(select count(*) as c2 from t2)
+select * from cte1,cte2;
+c1	c2
+3	1
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2 where cte1.c1 = 3;
+c1	c2
+drop procedure p;
+drop table t1,t2;

mysql-test/t/cte_recursive.test

@@ -2323,3 +2323,70 @@ RETURN
 SELECT func();
 
 DROP FUNCTION func;
+
+--echo #
+--echo # MDEV-17024: two materialized CTEs using the same recursive CTE
+--echo #
+
+create table t1 (id int);
+insert into t1 values (1), (2), (3);
+
+let $q=
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2;
+
+eval $q;
+eval explain extended $q;
+eval prepare stmt from "$q";
+execute stmt;
+execute stmt;
+
+create table t2 (c1 int, c2 int);
+eval create procedure p() insert into t2 $q;
+call p();
+select * from t2;
+
+let $q1=
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1;
+
+eval $q1;
+
+let $q2=
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from t1),
+cte2 as
+(select count(*) as c2 from t2)
+select * from cte1,cte2;
+
+eval $q2;
+
+let $q3=
+with recursive
+rcte(a) as
+(select 1 union select cast(a+1 as unsigned) from rcte where a < 10),
+cte1 as
+(select count(*) as c1 from rcte,t1 where a between 3 and 5 and id=a-3),
+cte2 as
+(select count(*) as c2 from rcte,t1 where a between 7 and 8 and id=a-7)
+select * from cte1, cte2 where cte1.c1 = 3;
+
+eval $q3;
+
+drop procedure p;
+drop table t1,t2;

sql/sql_base.cc

@@ -3295,6 +3295,15 @@ open_and_process_table(THD *thd, LEX *lex, TABLE_LIST *tables,
     */
     if (tables->with)
     {
+      if (tables->is_recursive_with_table() &&
+          !tables->is_with_table_recursive_reference())
+      {
+        tables->with->rec_outer_references++;
+        With_element *with_elem= tables->with;
+        while ((with_elem= with_elem->get_next_mutually_recursive()) !=
+               tables->with)
+	  with_elem->rec_outer_references++;
+      }
       if (tables->set_as_with_table(thd, tables->with))
         DBUG_RETURN(1);
       else

sql/sql_class.h

@@ -5095,10 +5095,16 @@ class select_union_recursive :public select_union
   TABLE *first_rec_table_to_update;
   /* The temporary tables used for recursive table references */
   List<TABLE> rec_tables;
+  /*
+    The count of how many times cleanup() was called with cleaned==false
+    for the unit specifying the recursive CTE for which this object was created
+    or for the unit specifying a CTE that mutually recursive with this CTE.
+  */
+  uint cleanup_count;
 
   select_union_recursive(THD *thd_arg):
     select_union(thd_arg),
-    incr_table(0), first_rec_table_to_update(0) {};
+    incr_table(0), first_rec_table_to_update(0), cleanup_count(0) {};
 
   int send_data(List<Item> &items);
   bool create_result_table(THD *thd, List<Item> *column_types,

sql/sql_cte.h

@@ -98,7 +98,14 @@ class With_element : public Sql_alloc
     for the definition of this element
   */
   bool is_recursive;
-
+  /*
+    For a simple recursive CTE: the number of references to the CTE from
+    outside of the CTE specification.
+    For a CTE mutually recursive with other CTEs : the total number of
+    references to all these CTEs outside of their specification.
+    Each of these mutually recursive CTEs has the same value in this field.
+  */
+  uint rec_outer_references;
   /*
     Any non-recursive select in the specification of a recursive
     with element is a called anchor. In the case mutually recursive
@@ -140,7 +147,7 @@ class With_element : public Sql_alloc
       top_level_dep_map(0), sq_rec_ref(NULL),
       next_mutually_recursive(NULL), references(0), 
       query_name(name), column_list(list), spec(unit),
-      is_recursive(false), with_anchor(false),
+      is_recursive(false), rec_outer_references(0), with_anchor(false),
       level(0), rec_result(NULL)
   { unit->with_element= this; }
 

sql/sql_derived.cc

@@ -1083,6 +1083,7 @@ bool mysql_derived_fill(THD *thd, LEX *lex, TABLE_LIST *derived)
   DBUG_ASSERT(derived->table && derived->table->is_created());
   select_union *derived_result= derived->derived_result;
   SELECT_LEX *save_current_select= lex->current_select;
+  bool derived_recursive_is_filled= false;
 
   if (derived_is_recursive)
   {
@@ -1095,6 +1096,7 @@ bool mysql_derived_fill(THD *thd, LEX *lex, TABLE_LIST *derived)
     {
       /* In this case all iteration are performed */
       res= derived->fill_recursive(thd);
+      derived_recursive_is_filled= true;
     }
   }
   else if (unit->is_union())
@@ -1150,7 +1152,9 @@ bool mysql_derived_fill(THD *thd, LEX *lex, TABLE_LIST *derived)
     }
   }
 
-  if (res || (!lex->describe && !derived_is_recursive))
+  if (res || (!lex->describe &&
+              (!derived_is_recursive ||
+               derived_recursive_is_filled)))
     unit->cleanup();
   lex->current_select= save_current_select;
 

sql/sql_union.cc

@@ -1337,6 +1337,37 @@ bool st_select_lex_unit::cleanup()
   {
     DBUG_RETURN(FALSE);
   }
+  /*
+    When processing a PS/SP or an EXPLAIN command cleanup of a unit can
+    be performed immediately when the unit is reached in the cleanup
+    traversal initiated by the cleanup of the main unit.
+  */
+  if (!thd->stmt_arena->is_stmt_prepare() && !thd->lex->describe &&
+      with_element && with_element->is_recursive && union_result)
+  {
+    select_union_recursive *result= with_element->rec_result;
+    if (++result->cleanup_count == with_element->rec_outer_references)
+    {
+      /*
+        Perform cleanup for with_element and for all with elements
+        mutually recursive with it.
+      */
+      cleaned= 1;
+      with_element->get_next_mutually_recursive()->spec->cleanup();
+    }
+    else
+    {
+      /*
+        Just increment by 1 cleanup_count for with_element and
+        for all with elements mutually recursive with it.
+      */
+      With_element *with_elem= with_element;
+      while ((with_elem= with_elem->get_next_mutually_recursive()) !=
+             with_element)
+        with_elem->rec_result->cleanup_count++;
+      DBUG_RETURN(FALSE);
+    }
+  }
   cleaned= 1;
 
   for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
@@ -1367,7 +1398,7 @@ bool st_select_lex_unit::cleanup()
 
   if (with_element && with_element->is_recursive)
   {
-    if (union_result )
+    if (union_result)
     {
       ((select_union_recursive *) union_result)->cleanup();
       delete union_result;