Bug #31890 Partitions: ORDER BY DESC in InnoDB not working.

It's not InnoDB specific bug.
Error is in QUEUE code, about the way we handle queue->max_at_top.
It's either '0' or '-2' and we do '^' operation to get the proper
direction. Though queue->compare() function can return '-2' as
a result of comparison sometimes. So we'll get
queue->compare() ^ queue->max_at_top == 0 (when max_at_top is -2)
and _downheap() function code will go wrong way here:
...
    if (next_index < elements &&
        (queue->compare(queue->first_cmp_arg,
                        queue->root[next_index]+offset_to_key,
                        queue->root[next_index+1]+offset_to_key) ^
         queue->max_at_top) > 0)
      next_index++;
...

Fixed by changing max_at_top to be either 1 or -1, doing
'* max_at_top' to get proper direction.


include/queues.h:
  Bug #31890 Partitions: ORDER BY DESC in InnoDB not working
  
  max_at_top policy changed
mysql-test/r/partition.result:
  Bug #31890 Partitions: ORDER BY DESC in InnoDB not working
  
  test result
mysql-test/t/partition.test:
  Bug #31890 Partitions: ORDER BY DESC in InnoDB not working
  
  test case
mysys/queues.c:
  Bug #31890 Partitions: ORDER BY DESC in InnoDB not working.
  
  queue->max_at_top policy changed - now it can either be '1' or '-1'.
  We multiply comparison result on max_at_top to get the proper
  direction.

1 files changed, 35 insertions, 0 deletions

diff --git a/mysql-test/r/partition.result b/mysql-test/r/partition.result
index b3a498ff0ab..589058c04a6 100644
--- a/mysql-test/r/partition.result
+++ b/mysql-test/r/partition.result
@@ -1296,4 +1296,39 @@ create table t1
 partition by key(s1) partitions 3;
 insert into t1 values (null,null);
 drop table t1;
+CREATE TABLE t1
+(int_column INT, char_column CHAR(5),
+PRIMARY KEY(char_column,int_column))
+PARTITION BY KEY(char_column,int_column)
+PARTITIONS 101;
+INSERT INTO t1 (int_column, char_column) VALUES
+(      39868 ,'zZZRW'),       
+(     545592 ,'zZzSD'),       
+(       4936 ,'zzzsT'),       
+(       9274 ,'ZzZSX'),       
+(     970185 ,'ZZzTN'),       
+(     786036 ,'zZzTO'),       
+(      37240 ,'zZzTv'),       
+(     313801 ,'zzzUM'),       
+(     782427 ,'ZZZva'),       
+(     907955 ,'zZZvP'),       
+(     453491 ,'zzZWV'),       
+(     756594 ,'ZZZXU'),       
+(     718061 ,'ZZzZH');
+SELECT * FROM t1 ORDER BY char_column DESC;
+int_column	char_column
+718061	ZZzZH
+756594	ZZZXU
+453491	zzZWV
+907955	zZZvP
+782427	ZZZva
+313801	zzzUM
+37240	zZzTv
+786036	zZzTO
+970185	ZZzTN
+9274	ZzZSX
+4936	zzzsT
+545592	zZzSD
+39868	zZZRW
+DROP TABLE t1;
 End of 5.1 tests