[PATCH] Use cache in org-up-heading-safe

[Ihor Radchenko <yantar92@gmail.com>]

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Hello,

While testing another patch for agenda fontification, I noticed that
agenda can spend up to half!! time doing org-up-heading-safe. Mostly
inside queries for inherited tags and properties.

I managed to make org-up-heading-safe up to 50x faster using position
cache.

If this patch also works for others, org-agenda-use-tag-inheritance
might become much less of an issue.

Benchmark:

1. (elp-instrument-function #'org-up-heading-safe)
2. Run agenda
3. (elp-results) ;; function, # calls, total time, avg time

Without cache:
org-up-heading-safe  27555       8.4234025759  0.0003056941

With cache, first run:
org-up-heading-safe  23227       0.5300747539  2.282...e-05

With cache, second run on unchanged buffer:
org-up-heading-safe  23227       0.1447754880  6.233...e-06

Best,
Ihor


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From fe1e7094a7b76ba6bf282c5c4409a32b36827d56 Mon Sep 17 00:00:00 2001
Message-Id: <fe1e7094a7b76ba6bf282c5c4409a32b36827d56.1620140628.git.yantar92@gmail.com>
From: Ihor Radchenko <yantar92@gmail.com>
Date: Tue, 4 May 2021 22:55:14 +0800
Subject: [PATCH] Use cache in org-up-heading-safe

* lisp/org.el (org-up-heading-safe): Use buffer-local cache to store
positions of parent headings.  The cache is invalidated when buffer
text is changed, according to `buffer-chars-modified-tick'.
(org--up-heading-cache):  Buffer-local hash-table storing the cache.
(org--up-heading-cache-tick):  The buffer modification state for
currently active `org--up-heading-cache'.

The optimisation is critical when running agenda or org-entry-get
queries using property/tag inheritance.  In such scenarios
`org-up-heading-safe' can be called thousands of times.  For example,
building todo agenda on large number of headings lead to the following
benchmark results:

Benchmark:

1. (elp-instrument-function #'org-up-heading-safe)
2. Run agenda
3. (elp-results) ;; function, # calls, total time, avg time

Without cache:
org-up-heading-safe  27555       8.4234025759  0.0003056941

With cache, first run:
org-up-heading-safe  23227       0.5300747539  2.282...e-05

With cache, second run on unchanged buffer:
org-up-heading-safe  23227       0.1447754880  6.233...e-06

The final speedup is 1-2 orders of magnitude (~15-56 times).
---
 lisp/org.el | 43 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index b8678359f..4385903ee 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -19434,6 +19434,10 @@ (defun org-up-heading-all (arg)
 With argument, move up ARG levels."
   (outline-up-heading arg t))
 
+(defvar-local org--up-heading-cache (make-hash-table)
+  "Buffer-local `org-up-heading-safe' cache.")
+(defvar-local org--up-heading-cache-tick nil
+  "Buffer `buffer-chars-modified-tick' in `org--up-heading-cache'.")
 (defun org-up-heading-safe ()
   "Move to the heading line of which the present line is a subheading.
 This version will not throw an error.  It will return the level of the
@@ -19443,10 +19447,41 @@ (defun org-up-heading-safe ()
 because it relies on stars being the outline starters.  This can really
 make a significant difference in outlines with very many siblings."
   (when (ignore-errors (org-back-to-heading t))
-    (let ((level-up (1- (funcall outline-level))))
-      (and (> level-up 0)
-	   (re-search-backward (format "^\\*\\{1,%d\\} " level-up) nil t)
-	   (funcall outline-level)))))
+    (let ((level-cache (gethash (point) org--up-heading-cache)))
+      (if (and level-cache
+               (eq (buffer-chars-modified-tick) org--up-heading-cache-tick))
+          (when (<= (point-min) level-cache (point-max))
+            ;; Parent is inside accessible part of the buffer.
+            (progn (goto-char level-cache)
+                   (funcall outline-level)))
+        ;; Buffer modified.  Invalidate cache.
+        (when level-cache
+          (clrhash org--up-heading-cache)
+          (setq-local org--up-heading-cache-tick
+                      (buffer-chars-modified-tick)))
+        (let ((level-up (1- (funcall outline-level)))
+              (pos (point)))
+          (let (result)
+            (setq result
+                  (and (> level-up 0)
+	               (re-search-backward
+                        (format "^\\*\\{1,%d\\} " level-up) nil t)
+	               (funcall outline-level)))
+            (when result
+              (puthash pos (point) org--up-heading-cache))))))))
+;; (defun org-up-heading-safe ()
+;;   "Move to the heading line of which the present line is a subheading.
+;; This version will not throw an error.  It will return the level of the
+;; headline found, or nil if no higher level is found.
+
+;; Also, this function will be a lot faster than `outline-up-heading',
+;; because it relies on stars being the outline starters.  This can really
+;; make a significant difference in outlines with very many siblings."
+;;   (when (ignore-errors (org-back-to-heading t))
+;;     (let ((level-up (1- (funcall outline-level))))
+;;       (and (> level-up 0)
+;; 	   (re-search-backward (format "^\\*\\{1,%d\\} " level-up) nil t)
+;; 	   (funcall outline-level)))))
 
 (defun org-up-heading-or-point-min ()
   "Move to the heading line of which the present is a subheading, or point-min.
-- 
2.26.3