TokuDB sorting time different between ASC vs DESC - mysql

Question

This is MariaDB + TokuDB 7.1 community downloaded from Tokutek. Please accept my ignorance if this is normal behavior but I have a question about sorting results. I'm experiencing huge time difference in sorting between the two sort directions - ascending and descending:
SELECT sql_no_cache id, createts, deleted
FROM sort_test
WHERE createts > '2000098'
ORDER BY createts asc
+---------+----------+---------+
| id | createts | deleted |
+---------+----------+---------+
| 1999999 | 2000099 | NULL |
| 2000000 | 2000100 | NULL |
+---------+----------+---------+
2 rows in set (0.00 sec)
SELECT sql_no_cache id, createts, deleted
FROM sort_test
WHERE createts > '2000098'
ORDER BY createts desc
+---------+----------+---------+
| id | createts | deleted |
+---------+----------+---------+
| 2000000 | 2000100 | NULL |
| 1999999 | 2000099 | NULL |
+---------+----------+---------+
2 rows in set (0.55 sec)
Below I present my simplified test case. Here is the table:
CREATE TABLE `sort_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`createts` int(11) DEFAULT NULL,
`deleted` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `idx_createts` (`createts`)
) ENGINE=TokuDB
Here I populate the table with 2 million rows using this procedure:
delimiter ;;
drop procedure if exists sort_test_populate;;
create procedure sort_test_populate()
begin
DECLARE int_val INT DEFAULT 1;
myloop : LOOP
if (int_val > 2000000) THEN
LEAVE myloop;
end if;
insert into sort_test (id, createts) values (int_val, int_val+100);
set int_val = int_val +1;
end loop;
end;;
call sort_test_populate();;
Query OK, 1 row affected (28 min 2.80 sec)
Here are my test queries again:
SELECT sql_no_cache id, createts, deleted
FROM sort_test
WHERE createts > '2000098'
ORDER BY createts asc
2 rows in set (0.00 sec)
SELECT sql_no_cache id, createts, deleted
FROM sort_test
WHERE createts > '2000098'
ORDER BY createts desc
2 rows in set (0.55 sec)
And here is the "explain extended" result, it's identical for both queries:
+------+-------------+-----------+-------+---------------+--------------+---------+------+------+----------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+------+-------------+-----------+-------+---------------+--------------+---------+------+------+----------+-------------+
| 1 | SIMPLE | sort_test | range | idx_createts | idx_createts | 5 | NULL | 2 | 100.00 | Using where |
+------+-------------+-----------+-------+---------------+--------------+---------+------+------+----------+-------------+
Please note that this is not my exact data I'm working with, that would be too much to include here. I just wanted to create some test data to demonstrate the problem. My question is - why it's behaving like this and how to make the descending order query faster?

Answer 1

This is a known bug with Index Condition Pushdown (ICP). The workaround is to disable ICP by setting the optimizer_switch either globally or within the session executing this query.
mysql> SET optimizer_switch='index_condition_pushdown=off';
(full disclosure, I'm an employee at Tokutek, makers of TokuDB)