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Slow operations on buffers of tens of megabytes


From: Alexandre Oliva
Subject: Slow operations on buffers of tens of megabytes
Date: Sun, 05 Nov 2006 03:37:06 -0200
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.90 (gnu/linux)

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

I use gnus to read my e-mail, and most of my messages are in nnfolder
groups.  This means lots and lots of messages are kept in a single
mbox-like file.  A few commonly-used groups have their e-mail stored
in files/buffers with a few tens of megabytes.

When I enter such a group, gnus goes over all unread or marked
messages searching for regular expressions to score them, i.e.,
determine whether the messages should be highlighted, hidden,
discarded, etc.

XEmacs 21.5.27 with xemacs-sumo 20060510 (including gnus 5.10) enters
such buffers very quickly, and only gets really slow for buffers that
exceed hundreds of megabytes, with tens of thounsands of e-mails.

In GNU Emacs 22.0.90.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2006-11-02 on free
X server distributor `The X.Org Foundation', version 11.0.70101000
configured using `configure '--prefix=/home/aoliva/test/emacs-22.0.90' 
'--exec-prefix=/home/aoliva/test/emacs-22.0.90/H-x86_64-linux-gnu' 'CC=ccache 
gcc -fno-working-directory -m64''

using the built-in gnus 5.11, it takes minutes to enter groups with
just a few hundred messages and just a few tens of megabytes in the
underlying buffer/file, where XEmacs takes less than 10 seconds.

Scoring of the messages closer to the beginning of the buffer is fast,
but as we move to higher-numbered messages, that are closer to the end
of such big files/buffers, gnus will only score 2-3 messages per
minute, and that's what kills performance.

I can't tell whether it is general big-buffer management that is
causing such slow downs, or if it's regular expression searching, or
some such, but this slow down is severely impacting my ability to
switch back to GNU Emacs :-(

I've historically switched back and forth as new major releases came
up, even though I felt more at home at GNU Emacs.  However, last time
I used GNU Emacs for mail reading, I still used the nnml back end,
instead of nnfolder, and nnml keeps each message in a separate file,
so it was not affected by this problem.

However, since that was much slower to enter groups on both Emacsen,
because folders were fragmented, at some point in the last few months
I switched to nnfolder, and that also had a great impact on my mail
backup times :-)

I hope this is enough information to figure out whom might help me
understand what the problem is and how I might be able to overcome it,
perhaps even helping fix it in GNU Emacs.

Thanks in advance,


Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
FSF Latin America Board Member         http://www.fsfla.org/
Red Hat Compiler Engineer   address@hidden, gcc.gnu.org}
Free Software Evangelist  address@hidden, gnu.org}




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