Fixed LP bug #925985.

If the flag 'optimize_join_buffer_size' is set to 'off' and the value
of the system variable 'join_buffer_size' is greater than the value of
the system variable 'join_buffer_space_limit' than no join cache can
be employed to join tables of the executed query.
A bug in the function JOIN_CACHE::alloc_buffer allowed to use join
buffer even in this case while another bug in the function 
revise_cache_usage could cause a crash of the server in this case if the
chosen execution plan for the query contained outer join or semi-join
operation.  

mysql-test/r/join_cache.result

@@ -5534,4 +5534,39 @@ we
 set join_cache_level = default;
 set optimizer_switch=@tmp_optimizer_switch;
 DROP TABLE t1,t2,t3;
+#
+# Bug #925985: LEFT JOIN with optimize_join_buffer_size=off +
+#              join_buffer_size > join_buffer_space_limit
+#
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (5), (3);
+CREATE TABLE t2 (a int, b int);
+INSERT INTO t2 VALUES
+(3,30), (1,10), (7,70), (2,20),
+(3,31), (1,11), (7,71), (2,21),
+(3,32), (1,12), (7,72), (2,22);
+CREATE TABLE t3 (b int, c int);
+INSERT INTO t3 VALUES (32, 302), (42,400), (30,300);
+set @tmp_optimizer_switch=@@optimizer_switch;
+set optimizer_switch='optimize_join_buffer_size=off';
+set join_buffer_space_limit=4096;
+set join_buffer_size=4096*2;
+set join_cache_level=2;
+set optimizer_switch='outer_join_with_cache=on';
+EXPLAIN
+SELECT * FROM t1, t2 LEFT JOIN t3 ON t2.b=t3.b WHERE t1.a=t2.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (incremental, BNL join)
+SELECT * FROM t1, t2 LEFT JOIN t3 ON t2.b=t3.b WHERE t1.a=t2.a;
+a	a	b	b	c
+3	3	30	30	300
+3	3	31	NULL	NULL
+3	3	32	32	302
+set join_buffer_space_limit=default;
+set join_buffer_size=default;
+set join_cache_level=default;
+set optimizer_switch=@tmp_optimizer_switch;
+DROP TABLE t1,t2,t3;
 set @@optimizer_switch=@save_optimizer_switch;

mysql-test/t/join_cache.test

@@ -3547,5 +3547,40 @@ set optimizer_switch=@tmp_optimizer_switch;
 
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # Bug #925985: LEFT JOIN with optimize_join_buffer_size=off +
+--echo #              join_buffer_size > join_buffer_space_limit
+--echo #
+
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (5), (3);
+
+CREATE TABLE t2 (a int, b int);
+INSERT INTO t2 VALUES
+  (3,30), (1,10), (7,70), (2,20),
+  (3,31), (1,11), (7,71), (2,21),
+  (3,32), (1,12), (7,72), (2,22);
+
+CREATE TABLE t3 (b int, c int);
+INSERT INTO t3 VALUES (32, 302), (42,400), (30,300);
+
+set @tmp_optimizer_switch=@@optimizer_switch;
+set optimizer_switch='optimize_join_buffer_size=off';
+set join_buffer_space_limit=4096;
+set join_buffer_size=4096*2;
+set join_cache_level=2;
+set optimizer_switch='outer_join_with_cache=on';
+
+EXPLAIN
+SELECT * FROM t1, t2 LEFT JOIN t3 ON t2.b=t3.b WHERE t1.a=t2.a;
+SELECT * FROM t1, t2 LEFT JOIN t3 ON t2.b=t3.b WHERE t1.a=t2.a;
+  
+set join_buffer_space_limit=default;
+set join_buffer_size=default;
+set join_cache_level=default;
+set optimizer_switch=@tmp_optimizer_switch;
+
+DROP TABLE t1,t2,t3;
+
 # this must be the last command in the file
 set @@optimizer_switch=@save_optimizer_switch;

sql/sql_join_cache.cc

@@ -898,6 +898,8 @@ int JOIN_CACHE::alloc_buffer()
       curr_buff_space_sz+= cache->get_join_buffer_size();
     }
   }
+  curr_min_buff_space_sz+= min_buff_size;
+  curr_buff_space_sz+= buff_size;
 
   if (curr_min_buff_space_sz > join_buff_space_limit ||
       (curr_buff_space_sz > join_buff_space_limit &&

sql/sql_select.cc

@@ -8903,7 +8903,7 @@ void revise_cache_usage(JOIN_TAB *join_tab)
          first_inner;
          first_inner= first_inner->first_upper)           
     {
-      for (tab= end_tab-1; tab >= first_inner; tab--)
+      for (tab= end_tab; tab >= first_inner; tab--)
         set_join_cache_denial(tab);
       end_tab= first_inner;
     }
@@ -8911,7 +8911,7 @@ void revise_cache_usage(JOIN_TAB *join_tab)
   else if (join_tab->first_sj_inner_tab)
   {
     first_inner= join_tab->first_sj_inner_tab;
-    for (tab= join_tab-1; tab >= first_inner; tab--)
+    for (tab= join_tab; tab >= first_inner; tab--)
     {
       set_join_cache_denial(tab);
     }