btr0btr.h, btr0btr.c, row0purge.c:

  Backport from 4.0: fix the BLOB hang if the index tree is of height 1


innobase/row/row0purge.c:
  Backport from 4.0: fix the BLOB hang if the index tree is of height 1
innobase/btr/btr0btr.c:
  Backport from 4.0: fix the BLOB hang if the index tree is of height 1
innobase/include/btr0btr.h:
  Backport from 4.0: fix the BLOB hang if the index tree is of height 1

innobase/btr/btr0btr.c

@@ -116,7 +116,7 @@ btr_page_insert_fits(
 
 /******************************************************************
 Gets the root node of a tree and x-latches it. */
-static
+
 page_t*
 btr_root_get(
 /*=========*/

innobase/include/btr0btr.h

@@ -55,6 +55,15 @@ UNIQUE definition on secondary indexes when we decide if we can use the
 insert buffer to speed up inserts */
 #define BTR_IGNORE_SEC_UNIQUE	2048	
 
+/******************************************************************
+Gets the root node of a tree and x-latches it. */
+
+page_t*
+btr_root_get(
+/*=========*/
+				/* out: root page, x-latched */
+	dict_tree_t*	tree,	/* in: index tree */
+	mtr_t*		mtr);	/* in: mtr */
 /******************************************************************
 Gets a buffer page and declares its latching order level. */
 UNIV_INLINE

innobase/row/row0purge.c

@@ -429,6 +429,8 @@ row_purge_upd_exist_or_extern(
 
 			mtr_x_lock(dict_tree_get_lock(index->tree), &mtr);
 
+			btr_root_get(index->tree, &mtr);
+
 			/* We assume in purge of externally stored fields
 			that the space id of the undo log record is 0! */