diff -u /tmp/nm-btree-1.org /tmp/nm-btree.org
--- /tmp/nm-btree-1.org	2021-05-10 23:04:21.286395360 +0800
+++ /tmp/nm-btree.org	2021-05-10 23:02:17.586396326 +0800
@@ -1,3 +1,6 @@
+:PROPERTIES:
+:ID:       0aba93db-491d-46f7-b952-e138ba179a12
+:END:
 
 #+begin_src elisp :results none
 
@@ -38,6 +41,26 @@
 		(push props parents))))
 	  (and headings (cons headings count)))))))
 
+(defun nm-buffer-headings-reversed-cache (buffer)
+  (with-current-buffer buffer
+    (save-restriction
+      (save-excursion
+	(widen)
+	(goto-char (point-min))
+	(let ((count 0)
+	      (headings ())
+	      (parents ()))
+	  (while (re-search-forward org-outline-regexp-bol nil t)
+            (let ((cached (org-element--cache-find (line-beginning-position))))
+              (if (eq (org-element-property :begin cached) (line-beginning-position))
+                  (push cached headings)
+                (push (org-element-at-point) headings)))
+            
+            ;; (save-excursion
+            ;;   (beginning-of-line)
+            ;;   (org-element-at-point 'cached))
+            ))))))
+
 
 ;; binary search tree
 (defun nm-btree-new-node ()
@@ -103,6 +126,7 @@
 
 #+begin_src elisp
 (byte-compile #'nm-buffer-headings-reversed)
+(byte-compile #'nm-buffer-headings-reversed-cache)
 (byte-compile #'nm-btree-from-reversed)
 (byte-compile #'nm-btree-find-left)
 
@@ -125,13 +149,44 @@
 	     (let* ((scan-result1 (nm-buffer-headings-reversed buffer))
 		    (tree1 (nm-btree-from-reversed scan-result1)))
 	       tree1)))
+   (append '("scan using org-element-cache x10")
+           (progn
+             (let ((org-element-cache-sync-duration 1000.0))
+               (org-element-cache-reset)
+	       (org-element--cache-buffer-stealthly))
+	     (benchmark-run 10
+	       (nm-buffer-headings-reversed-cache buffer))))
+   (append '("populating the cache x1")
+	   (benchmark-run 1
+             (with-current-buffer buffer
+               ;; Disable async processing.
+               (let ((org-element-cache-sync-duration 1000.0))
+                 (org-element-cache-reset)
+	         (org-element--cache-buffer-stealthly)))))
    (append '("find random x10 000")
 	   (benchmark-run 10000
 	     (nm-btree-find-left tree (random lim))))
+   (append '("find random in org-element-cache x10 000")
+	   (benchmark-run 10000
+             (org-element-lineage
+	      (org-element--cache-find (random lim))
+              '(headlines) t)))
    (list "nodes" (cdr scan-result) "" "")))
 #+end_src
 
 #+RESULTS:
+| scan x10                                 |          1.693757321 | 0 |                 0.0 |
+| btree x10                                |          0.552682783 | 1 | 0.43690057000000593 |
+| scan+btree x10                           |   2.3174109880000002 | 0 |                 0.0 |
+| scan using org-element-cache x10         |   2.9140550789999997 | 0 |                 0.0 |
+| populating the cache x1                  |          10.83575134 | 9 |  3.9872376689999953 |
+| find random x10 000                      | 0.061988949999999994 | 0 |                 0.0 |
+| find random in org-element-cache x10 000 |          0.003262685 | 0 |                 0.0 |
+| nodes                                    |                16641 |   |                     |
+
+
+
+
 | scan x10            |   0.8611382689999999 | 0 |                 0.0 |
 | btree x10           |  0.07705962400000001 | 1 | 0.05648322199999978 |
 | scan+btree x10      |          0.940467238 | 1 | 0.05685373699999996 |

Diff finished.  Mon May 10 23:04:27 2021