MDEV-11722 main.join_cache fails in buildbot on very slow builders

The guilty part of the test checks for performance degradation on
a query with numerous joins on an empty table. The test expects
the query to take less than 1 second, and fails if it is not so
(which can happen on very slow builders).

The solution is to add more JOINs to the query. On a fixed server,
it should not have any noticeable impact on the query execution,
while on the unfixed version the query would take several times
longer (e.g. 6.5 sec vs 1.5 sec). Thus, we can increase the margin
for the error, and make the test fail when the query takes longer
than 5 seconds.

mysql-test/r/join_cache.result

@@ -5702,11 +5702,13 @@ LEFT JOIN t2 c1 ON c1.parent_id = t.id AND c1.col2 = "val"
   LEFT JOIN t2 c23 ON c23.parent_id = t.id AND c23.col2 = "val"
   LEFT JOIN t2 c24 ON c24.parent_id = t.id AND c24.col2 = "val"
   LEFT JOIN t2 c25 ON c25.parent_id = t.id AND c25.col2 = "val"
+  LEFT JOIN t2 c26 ON c26.parent_id = t.id AND c26.col2 = "val"
+  LEFT JOIN t2 c27 ON c27.parent_id = t.id AND c27.col2 = "val"
 ORDER BY 
 col1;
 id	col1
-select timestampdiff(second, @init_time, now()) <= 1;
-timestampdiff(second, @init_time, now()) <= 1
+select timestampdiff(second, @init_time, now()) <= 5;
+timestampdiff(second, @init_time, now()) <= 5
 1
 set join_cache_level=2;
 set @init_time:=now();
@@ -5738,11 +5740,13 @@ LEFT JOIN t2 c1 ON c1.parent_id = t.id AND c1.col2 = "val"
   LEFT JOIN t2 c23 ON c23.parent_id = t.id AND c23.col2 = "val"
   LEFT JOIN t2 c24 ON c24.parent_id = t.id AND c24.col2 = "val"
   LEFT JOIN t2 c25 ON c25.parent_id = t.id AND c25.col2 = "val"
+  LEFT JOIN t2 c26 ON c26.parent_id = t.id AND c26.col2 = "val"
+  LEFT JOIN t2 c27 ON c27.parent_id = t.id AND c27.col2 = "val"
 ORDER BY 
 col1;
 id	col1
-select timestampdiff(second, @init_time, now()) <= 1;
-timestampdiff(second, @init_time, now()) <= 1
+select timestampdiff(second, @init_time, now()) <= 5;
+timestampdiff(second, @init_time, now()) <= 5
 1
 EXPLAIN
 SELECT t.* 
@@ -5773,6 +5777,8 @@ LEFT JOIN t2 c1 ON c1.parent_id = t.id AND c1.col2 = "val"
   LEFT JOIN t2 c23 ON c23.parent_id = t.id AND c23.col2 = "val"
   LEFT JOIN t2 c24 ON c24.parent_id = t.id AND c24.col2 = "val"
   LEFT JOIN t2 c25 ON c25.parent_id = t.id AND c25.col2 = "val"
+  LEFT JOIN t2 c26 ON c26.parent_id = t.id AND c26.col2 = "val"
+  LEFT JOIN t2 c27 ON c27.parent_id = t.id AND c27.col2 = "val"
 ORDER BY 
 col1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
@@ -5802,6 +5808,8 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	c23	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (incremental, BNL join)
 1	SIMPLE	c24	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (incremental, BNL join)
 1	SIMPLE	c25	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (incremental, BNL join)
+1	SIMPLE	c26	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (incremental, BNL join)
+1	SIMPLE	c27	ALL	NULL	NULL	NULL	NULL	1	Using where; Using join buffer (incremental, BNL join)
 set join_buffer_size=default;
 set join_cache_level = default;
 DROP TABLE t1,t2;

mysql-test/t/join_cache.test

@@ -3709,9 +3709,11 @@ FROM
   LEFT JOIN t2 c23 ON c23.parent_id = t.id AND c23.col2 = "val"
   LEFT JOIN t2 c24 ON c24.parent_id = t.id AND c24.col2 = "val"
   LEFT JOIN t2 c25 ON c25.parent_id = t.id AND c25.col2 = "val"
+  LEFT JOIN t2 c26 ON c26.parent_id = t.id AND c26.col2 = "val"
+  LEFT JOIN t2 c27 ON c27.parent_id = t.id AND c27.col2 = "val"
 ORDER BY 
   col1;
-select timestampdiff(second, @init_time, now()) <= 1;
+select timestampdiff(second, @init_time, now()) <= 5;
 
 set join_cache_level=2;
 
@@ -3744,9 +3746,11 @@ FROM
   LEFT JOIN t2 c23 ON c23.parent_id = t.id AND c23.col2 = "val"
   LEFT JOIN t2 c24 ON c24.parent_id = t.id AND c24.col2 = "val"
   LEFT JOIN t2 c25 ON c25.parent_id = t.id AND c25.col2 = "val"
+  LEFT JOIN t2 c26 ON c26.parent_id = t.id AND c26.col2 = "val"
+  LEFT JOIN t2 c27 ON c27.parent_id = t.id AND c27.col2 = "val"
 ORDER BY 
   col1;
-select timestampdiff(second, @init_time, now()) <= 1;
+select timestampdiff(second, @init_time, now()) <= 5;
 
 EXPLAIN
 SELECT t.* 
@@ -3777,6 +3781,8 @@ FROM
   LEFT JOIN t2 c23 ON c23.parent_id = t.id AND c23.col2 = "val"
   LEFT JOIN t2 c24 ON c24.parent_id = t.id AND c24.col2 = "val"
   LEFT JOIN t2 c25 ON c25.parent_id = t.id AND c25.col2 = "val"
+  LEFT JOIN t2 c26 ON c26.parent_id = t.id AND c26.col2 = "val"
+  LEFT JOIN t2 c27 ON c27.parent_id = t.id AND c27.col2 = "val"
 ORDER BY 
   col1;