CODEWITHSUNDEEP
emacs
goofansu
goofansu

Reputation: 2277

How to improve emacs performance when view large file?

Emacs sometimes hangs when viewing large file. But it is fast with (global-font-lock-mode -1).

I'm using a fork of Prelude.

Emacs version: 24.3 cocoa System: OS X 10.8.4

Update: I found (setq jit-lock-defer-time 0.05) is a method to improve the scrolling speed.

Upvotes: 28

Views: 16464

Answers (4)

Alaa Ahmad M. Zakaria
Alaa Ahmad M. Zakaria

Reputation: 251

it may be trick workaround
M-x shell
then
less your_large_file.txt
and you can proceed

Upvotes: -2

Trey Jackson
Trey Jackson

Reputation: 74480

To help with large files, I've installed my own find-file-hook which turns on fundamental mode (avoids font-lock), turns off undo, and makes the buffer read-only just to avoid any accidental changes (making unnecessary backups of large files).

(defun my-find-file-check-make-large-file-read-only-hook ()
  "If a file is over a given size, make the buffer read only."
  (when (> (buffer-size) (* 1024 1024))
    (setq buffer-read-only t)
    (buffer-disable-undo)
    (fundamental-mode)))

(add-hook 'find-file-hook 'my-find-file-check-make-large-file-read-only-hook)

Obviously adjust the threshold value as you see fit.

Upvotes: 32

gavenkoa
gavenkoa

Reputation: 48893

I usually unroll long lines and indent by tags (like HTML, XML, JSON).

In order to make such operation possible I add:

(setq line-number-display-limit large-file-warning-threshold)
(setq line-number-display-limit-width 200)

(defun my--is-file-large ()
  "If buffer too large and my cause performance issue."
  (< large-file-warning-threshold (buffer-size)))

(define-derived-mode my-large-file-mode fundamental-mode "LargeFile"
  "Fixes performance issues in Emacs for large files."
  ;; (setq buffer-read-only t)
  (setq bidi-display-reordering nil)
  (jit-lock-mode nil)
  (buffer-disable-undo)
  (set (make-variable-buffer-local 'global-hl-line-mode) nil)
  (set (make-variable-buffer-local 'line-number-mode) nil)
  (set (make-variable-buffer-local 'column-number-mode) nil) )

(add-to-list 'magic-mode-alist (cons #'my--is-file-large #'my-large-file-mode))

Note that I don't use find-file-hooks as magic-mode-alist usually empty and have priority. If I add find-file-hooks it first validate XML file by nxml-mode and then switch to fundamental-mode.

I split line by regex, for XML it: C-M-% >< RET >NL< RET !.

After Emacs split long lines - it is possible to enable many *-modes and re-indent code.

Upvotes: 4

Alex Vorobiev
Alex Vorobiev

Reputation: 4359

If you need to work with really large files, you can use the View Large Files package which allows "viewing, editing and searching in large files in chunks." After requireing the package open large files with M-x vlfi.

Upvotes: 18

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