Re: Handling large files with emacs lisp?

[Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com>]

Oddly, when I tried today again, I saw constant time file access with ~
80MB/s across the 183MB installer of Libreoffice and 240-290 MB/s on a
repetitive text file. Most likely explanation: A bug in my test function
(e.g. accidentially inserted text length not being constant). A bit
embarassing here ^^'

On the other hand this shows me that Emacs Lisp is indeed usable for
general purpose processing.

kind regards, Klaus


2013/6/4 Jambunathan K <kjambunathan@gmail.com>

>
> May be you can steal some stuff from here.
>
>         http://elpa.gnu.org/packages/vlf.html
>
> It is a GNU ELPA package that you can install with M-x list-packages
> RET.
>
>
>
> Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:
>
> > Hello!
> >
> > Is there a method in emacs lisp to handle large files (hundreds of MB)
> > efficiently? I am looking specifically for a function that allows
> > processing file contents either sequentially or (better) with random
> > access.
> >
> > Looking through the code of `find-file' I found that
> > `insert-file-contents' and `insert-file-contents-literally' seem to be
> > pretty much the most low-level functions available to emacs-lisp. When
> > files go towards GB size however, inserting file contents is
> > undesirable even assuming 32bit emacs were able to handle such large
> > buffers.
> >
> > Using the BEG and END parameters of `insert-file-contents' however has
> > a linear time-dependence on BEG. So implementing buffered file
> > processing for large files by keeping only parts of the file in a
> > temporary buffer doesn't seem feasible either.
> >
> > I'd also be interested why there is this linear time dependence. Is
> > this a limitation of how fseek works or of how `insert-file-contents'
> > is implemented? I've read[1] that fseek "just updates pointers", so
> > random reads in a large file, especially on an SSD, should be
> > constant-time, but I couldn't find further verification.
> >
> > kind regards, Klaus
> >
> > PS: I'm well aware that I'm asking for something, that likely wasn't
> >     within the design goals of emacs lisp. It is interesting to push
> >     the limits though ;)
> >
> > ------------------------------------------------------------
> >
> > [1]
> https://groups.google.com/d/msg/comp.unix.aix/AXInTbcjsKo/qt-XnL12upgJ
>