Subject: bug#62780: 30.0.50; Redisplay gets slow when using Org tables + show-trailing-whitespace

From: Eli Zaretskii <[email-masked]>
Date: Tue, 11 Apr 2023 22:25:25 +0300

> From: Ihor Radchenko <[email-masked]>
> Date: Tue, 11 Apr 2023 18:52:43 +0000
> 
> 1. emacs -Q
> 2. M-x org-mode <RET>
> 3. M-x org-table-create <RET> 30x30 <RET>
> 4. M-: (setq show-trailing-whitespace t) <RET>
> 4. M-x org-table-insert-column <RET> (20x times)
> 5. M-> type something
> 6. Observe significant lag when typing. CPU profiler does not expose much.

show-trailing-whitespace disables quite a few redisplay optimizations,
including even the cursor-motion optimization (when nothing has
changed on display except the position of point).  And full thorough
redisplay becomes slow when you have relatively long lines, because
Emacs is forced to consider all of them.

In addition, org-table seems to put a large number of 'display'
properties (like, 2 per cell?), which also slows down redisplay.

Are you saying there's been a regression in Emacs 30 in this situation
wrt Emacs 29 and Emacs 28?  I don't think I see a regression in my
testing here.