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

[Maxim Nikulin]

On 04/05/2021 22:08, Ihor Radchenko wrote:
> 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.

I have not tested the patch due to I do not use agenda. My interest was 
stimulated solely by my attempts to make org-refile-get-targets faster.

I consider it as an improvement. I have noticed the only thing that must 
be fixed: comments with old variant of the function. Reaction to my 
other comments is optional.

In org-agenda.el org-up-heading-safe function is called only from 
org-find-top-headline. So the purpose of the dance with backward 
searches is to get top level headings. My expectation is that scan 
through the whole buffer and storing result in a structure that allows 
binary search of position (array, red-black tree, etc) may be even faster.

Alternatively lazily obtained position of top heading could be stored in 
cache to reduce number of iterations on org-find-top-line.

> +    (let ((level-cache (gethash (point) org--up-heading-cache)))
> +      (if (and level-cache
> +               (eq (buffer-chars-modified-tick) org--up-heading-cache-tick))

If buffer-chars-modified-tick is faster than gethash then reordering 
might result in very slight improvement of performance.

> +            ;; Parent is inside accessible part of the buffer.
> +            (progn (goto-char level-cache)
> +                   (funcall outline-level)))

I do not see any reason why outline level can not be cached in pair with 
position.

> +          (let (result)
> +            (setq result

I am not a lisp guru, so from my point of view this can be reduced to
(let ((result ...

> +                        (format "^\\*\\{1,%d\\} " level-up) nil t)

\t as an alternative to " " is used in org-refile.el,
e.g. "^\\*+[ \t]+". Unsure which variant is canonical one and I see that 
regexp is taken from original function, so no regression is expected.

> +;; (defun org-up-heading-safe ()
> +;;   "Move to the heading line of which the present line is a subheading.

Clean-up here is required, other notes may be ignored.