index_read_map(HA_READ_BEFORE_KEY) does not work in reverse column family

[spetrunia]

This is a continuation of issue #16.

Let's work with the same dataset

create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1(a int);
insert into t1 select A.a + B.a* 10 + C.a * 100 from t0 A, t0 B, t0 C;

create table t2 (
  pk int not null,
  a  int not null,
  b  int not null,
  primary key(pk),
  key(a) comment 'rev:cf1'
) engine=rocksdb;
insert into t2 select A.a, FLOOR(A.a/10), A.a from t1 A;

Try this:

MySQL [test]> select max(a) from t2 where a < 2;
+--------+
| max(a) |
+--------+
|      2 |
+--------+

This is apparently wrong. For comparison, the same without the index:

MySQL [test]> create table t3 as select * from t2;
Query OK, 1000 rows affected (0.58 sec)
Records: 1000  Duplicates: 0  Warnings: 0

MySQL [test]> select max(a) from t3 where a < 2;
+--------+
| max(a) |
+--------+
|      1 |
+--------+

[spetrunia]

https://reviews.facebook.net/D35331