bug#2688 - Wrong index_merge query results for BDB table with variable length primary key.

dded code to clear the tail of the reference buffer if the actual key length 
is less than the maximum key length.

mysql-test/r/bdb.result

@@ -1190,3 +1190,21 @@ a
 A
 a
 drop table t1;
+create table t1 (
+pk1 varchar(8) not null default '',
+pk2 varchar(4) not null default '',
+key1 int(11) default null,
+key2 int(11) default null,
+primary key  (pk1,pk2),
+key key1 (key1),
+key key2 (key2)) engine=bdb;
+insert into t1 values ('','empt',2,2),  ('a','a--a',2,2),
+('bb','b--b',2,2),  ('ccc','c--c',2,2),  ('dddd','d--d',2,2);
+select * from t1 force index(key1, key2) where key1 < 3 or key2 < 3;
+pk1	pk2	key1	key2
+	empt	2	2
+a	a--a	2	2
+bb	b--b	2	2
+ccc	c--c	2	2
+dddd	d--d	2	2
+drop table t1;

mysql-test/t/bdb.test

@@ -829,3 +829,21 @@ alter table t1 modify a char(10) binary;
 explain select a from t1;
 select a from t1;
 drop table t1;
+
+#
+# bug#2688 - Wrong index_merge query results for BDB table with variable length primary key
+#
+
+create table t1 (
+  pk1 varchar(8) not null default '',
+  pk2 varchar(4) not null default '',
+  key1 int(11) default null,
+  key2 int(11) default null,
+  primary key  (pk1,pk2),
+  key key1 (key1),
+  key key2 (key2)) engine=bdb;
+insert into t1 values ('','empt',2,2),  ('a','a--a',2,2),
+  ('bb','b--b',2,2),  ('ccc','c--c',2,2),  ('dddd','d--d',2,2);
+select * from t1 force index(key1, key2) where key1 < 3 or key2 < 3;
+drop table t1;
+

sql/ha_berkeley.cc

@@ -1611,13 +1611,44 @@ int ha_berkeley::rnd_pos(byte * buf, byte *pos)
 		       (char*) buf, primary_key, &current_row, (DBT*) 0, 0));
 }
 
+/*
+  Set a reference to the current record in (ref,ref_length).
+
+  SYNOPSIS
+    ha_berkeley::position()
+    record                      The current record buffer
+
+  DESCRIPTION
+    The BDB handler stores the primary key in (ref,ref_length).
+    There is either an explicit primary key, or an implicit (hidden)
+    primary key.
+    During open(), 'ref_length' is calculated as the maximum primary
+    key length. When an actual key is shorter than that, the rest of
+    the buffer must be cleared out. The row cannot be identified, if
+    garbage follows behind the end of the key. There is no length
+    field for the current key, so that the whole ref_length is used
+    for comparison.
+
+  RETURN
+    nothing
+*/
+
 void ha_berkeley::position(const byte *record)
 {
   DBT key;
+  DBUG_ENTER("ha_berkeley::position");
   if (hidden_primary_key)
+  {
+    DBUG_ASSERT(ref_length == BDB_HIDDEN_PRIMARY_KEY_LENGTH);
     memcpy_fixed(ref, (char*) current_ident, BDB_HIDDEN_PRIMARY_KEY_LENGTH);
+  }
   else
+  {
     create_key(&key, primary_key, (char*) ref, record);
+    if (key.size < ref_length)
+      bzero(ref + key.size, ref_length - key.size);
+  }
+  DBUG_VOID_RETURN;
 }