Bug#26996 - Update of a Field in a Memory Table ends with wrong result

Using a MEMORY table BTREE index for scanning for updatable rows
could lead to an infinite loop.

Everytime a key was inserted into a btree index, the position
in the index scan was cleared. The search started from the
beginning and found the same key again.

Now we do not clear the position on key insert an more.

heap/hp_write.c

@@ -106,7 +106,6 @@ int hp_rb_write_key(HP_INFO *info, HP_KEYDEF *keyinfo, const byte *record,
   heap_rb_param custom_arg;
   uint old_allocated;
 
-  info->last_pos= NULL; /* For heap_rnext/heap_rprev */
   custom_arg.keyseg= keyinfo->seg;
   custom_arg.key_length= hp_rb_make_key(keyinfo, info->recbuf, record, recpos);
   if (keyinfo->flag & HA_NOSAME)

mysql-test/r/heap_btree.result

@@ -280,4 +280,19 @@ a
 1
 1
 drop table t1;
+CREATE TABLE t1 (
+c1 CHAR(3),
+c2 INTEGER,
+KEY USING BTREE(c1),
+KEY USING BTREE(c2)
+) ENGINE= MEMORY;
+INSERT INTO t1 VALUES ('ABC',0), ('A',0), ('B',0), ('C',0);
+UPDATE t1 SET c2= c2 + 1 WHERE c1 = 'A';
+SELECT * FROM t1;
+c1	c2
+ABC	0
+A	1
+B	0
+C	0
+DROP TABLE t1;
 End of 4.1 tests

mysql-test/t/heap_btree.test

@@ -182,4 +182,18 @@ delete from t1 where a >= 2;
 select a from t1 order by a;
 drop table t1;
 
+#
+# Bug#26996 - Update of a Field in a Memory Table ends with wrong result
+#
+CREATE TABLE t1 (
+  c1 CHAR(3),
+  c2 INTEGER,
+  KEY USING BTREE(c1),
+  KEY USING BTREE(c2)
+) ENGINE= MEMORY;
+INSERT INTO t1 VALUES ('ABC',0), ('A',0), ('B',0), ('C',0);
+UPDATE t1 SET c2= c2 + 1 WHERE c1 = 'A';
+SELECT * FROM t1;
+DROP TABLE t1;
+
 --echo End of 4.1 tests