MariaRocks port: fix rocksdb.bloomfilter3 test

In MySQL 5.6, QUICK_SELECT_DESC calls handler->set_end_range() to
inform the storage engine about the bounds of the range being scanned.

MariaDB doesn't have that (handler::set_end_range call was back-ported
but it is not called from QUICK_SELECT_DESC).
Instead, it got prepare_*scan() methods from TokuDB.

Implement these methods so that MyRocks has information about the range
end.

Author: spetrunia

storage/rocksdb/ha_rocksdb.cc

@@ -6528,6 +6528,23 @@ int ha_rocksdb::read_range_first(const key_range* const start_key,
 }
 
 
+int ha_rocksdb::prepare_index_scan()
+{
+  range_key_part= table->key_info[active_index].key_part;
+  set_end_range(NULL);
+  return 0;
+}
+
+
+int ha_rocksdb::prepare_range_scan(const key_range *start_key,
+                                    const key_range *end_key)
+{
+  range_key_part= table->key_info[active_index].key_part;
+  set_end_range(end_key);
+  return 0;
+}
+
+
 int ha_rocksdb::index_read_map(uchar* const buf, const uchar* const key,
                                key_part_map keypart_map,
                                enum ha_rkey_function find_flag)

storage/rocksdb/ha_rocksdb.h

@@ -576,6 +576,17 @@ class ha_rocksdb: public my_core::handler
   void update_stats(void);
 
 public:
+  /*
+    The following two are currently only used for getting the range bounds
+    from QUICK_SELECT_DESC.
+    We don't need to implement prepare_index_key_scan[_map] because it is
+    only used with HA_READ_KEY_EXACT and HA_READ_PREFIX_LAST where one
+    can infer the bounds of the range being scanned, anyway.
+  */
+  int prepare_index_scan() override;
+  int prepare_range_scan(const key_range *start_key,
+                         const key_range *end_key) override;
+
   /*
     Controls whether writes include checksums. This is updated from the session variable
     at the start of each query.

storage/rocksdb/mysql-test/rocksdb/r/bloomfilter3.result

@@ -101,20 +101,20 @@ insert into t1 values (21,2,2,0x12FFFFFFFFFF,1);
 explain 
 select * from t1 where kp0=1 and kp1=1 and kp2=0x12FFFFFFFFFF order by kp3 desc;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	kp12	kp12	28	NULL	#	Using where; Using index
+1	SIMPLE	t1	ref	kp12	kp12	20	const,const,const	#	Using where; Using index
 show status like '%rocksdb_bloom_filter_prefix%';
 Variable_name	Value
-rocksdb_bloom_filter_prefix_checked	0
-rocksdb_bloom_filter_prefix_useful	0
+Rocksdb_bloom_filter_prefix_checked	0
+Rocksdb_bloom_filter_prefix_useful	0
 select variable_value into @c from information_schema.global_status where variable_name='rocksdb_bloom_filter_prefix_checked';
 select * from t1 where kp0=1 and kp1=1 and kp2=0x12FFFFFFFFFF order by kp3 desc;
 pk	kp0	kp1	kp2	kp3
 11	1	1	20890720927743	1
 10	1	1	20890720927743	1
 show status like '%rocksdb_bloom_filter_prefix%';
 Variable_name	Value
-rocksdb_bloom_filter_prefix_checked	0
-rocksdb_bloom_filter_prefix_useful	0
+Rocksdb_bloom_filter_prefix_checked	0
+Rocksdb_bloom_filter_prefix_useful	0
 # The following MUST show TRUE:
 select case when variable_value-@c = 0 then 'true' else 'false' end from information_schema.global_status where variable_name='rocksdb_bloom_filter_prefix_checked';
 case when variable_value-@c = 0 then 'true' else 'false' end