footnote fontify causing massive slowdown

[Derek Feichtinger <derek.feichtinger@psi.ch>]

While diagnosing a server condition, I was listing parts of a system log
via a babel expression. The 130 lines in the babel output are wrapped in
an example block. This block caused massive slowdown of scrolling and
other operations.

Using the emacs profiler I see:

- redisplay_internal (C function) 8232  88%
  - jit-lock-function 8226  88%
   - jit-lock-fontify-now 8226  88%
    - funcall 8226  88%
     - #<compiled 0x1cc274f>                                      8226  88%
      - run-hook-with-args 8226  88%
       - font-lock-fontify-region 8226  88%
        - font-lock-default-fontify-region 8226  88%
         - font-lock-fontify-keywords-region 8226  88%
          - org-activate-footnote-links 8158  87%
           - org-footnote-next-reference-or-definition 8158  87%
            - byte-code 8158  87%
             - org-footnote-at-reference-p 4114  44%
              - org-footnote-in-valid-context-p 4106  44%
               + org-inside-LaTeX-fragment-p 2380  25%
               + org-in-block-p 1563  16%
               + org-in-verbatim-emphasis 159   1%
                 org-at-comment-p 4   0%

Checking for footnote pattern matches (org-footnote-re) in the wrapped 
block, I see that
every line matches based on the very simple and trivial pattern of
number enclosed in angular brackets, so all the process numbers
following the "sshd" in these lines like "sshd[1234]" do match and cause 
load.

#################
     /var/log/secure-20151129:Nov 23 02:25:36 some-host sshd[20089]: 
Rhosts authentication refused for userXYZ: bad ownership or modes for 
home directory.
     /var/log/secure-20151129:Nov 23 02:25:36 some-host sshd[20089]: 
Rhosts authentication refused for userXYZ: bad ownership or modes for 
home directory.
     /var/log/secure-20151129:Nov 23 02:25:41 some-host sshd[20089]: 
pam_ldap: error trying to bind as user "xxxxx" (Invalid credentials)
#################

Since this kind of pattern is so common in logs and 130 lines are really 
not a large number, it makes it hard to use
org for this purpose. Can this be turned off selectively, or can it be
prevented in example blocks?

Using [8.3.2 (8.3.2-37-gd45217-elpaplus @ 
/home/dfeich/.emacs.d/elpa/org-plus-contrib-20151116/)] with GNU Emacs 
24.5.1.

Best regards,
Derek




-- 
Paul Scherrer Institut
Dr. Derek Feichtinger                   Phone:   +41 56 310 47 33
Section Head Scientific Computing       Email: derek.feichtinger@psi.ch
Building/Room No. WHGA/U126
CH-5232 Villigen PSI