ls -l takes a forever to finish.

[Mark Evans]

this program seems to have the same issues with it.

Thanks
Mark


----- Original Message ----- 
From: "cpghost" <cpghost at cordula.ws>
To: "Bill Moran" <wmoran at potentialtech.com>
Cc: "Wojciech Puchar" <wojtek at wojtek.tensor.gdynia.pl>; 
<questions at freebsd.org>; "Mark Evans" <mbe2 at bayou.com>
Sent: Thursday, November 29, 2007 8:42 AM
Subject: Re: ls -l takes a forever to finish.


> On Thu, 29 Nov 2007 08:42:44 -0500
> Bill Moran <wmoran at potentialtech.com> wrote:
>
>> In response to Wojciech Puchar <wojtek at wojtek.tensor.gdynia.pl>:
>>
>> > > ls | wc
>> >
>> > strange. i did
>> >
>> > [wojtek at wojtek ~/b]$ a=0;while [ $a -lt 10000 ];do mkdir
>> > $a;a=$[a+1];done
>> >
>> > completed <25 seconds on 1Ghz CPU
>> >
>> > ls takes 0.1 seconds user time, ls -l takes 0.3 second user time.
>> >
>> > unless you have 486/33 or slower system there is something wrong.
>>
>> Another possible scenario is that the directory is badly fragmented.
>> Unless something has changed since I last researched this (which is
>> possible) FreeBSD doesn't manage directory fragmentation during use.
>> If you're constantly adding and removing files, it's possible that
>> the directory entry is such a mess that it takes ls a long time to
>> process it.
>
> Yes, that's also possible. But sorting is really the culprit here:
> it *is* possible to create a directory with filenames in such a way
> that it triggers Quicksort's O(N^2) worst case instead of O(N log N).
>
> The following Python (2.5) program calls "ls -lf" and sorts its output
> with Python's own stable sort() routine (which is NOT qsort(3)). On a
> directory with 44,000 entries, it runs orders of magnitude faster than
> "ls -l", even though it has to use the decorate-sort-undecorate idiom
> to sort the output according according the filename, and it is
> interpreted rather than compiled!
>
> I guess that replacing qsort(3) in
> /usr/src/lib/libc/gen/fts.c:fts_sort()
> with another sort algorithm which doesn't
> expose this anomaly would solve that problem.
>
> --------------------- cut here ------------------ cut here ------------
>
> #!/usr/bin/env python
> # sortls.py -- sort output of ls -lf with python's stable sort routine.
>
> import os
>
> def sort_ls_lf(path):
>    "Sort the output of ls -lf path"
>    os.chdir(path)
>    lines = os.popen("ls -lf", "r").readlines()
>    dsu = [ (line.split()[-1], line) for line in lines ]
>    dsu.sort()
>    return ''.join(tupl[1] for tupl in dsu)
>
> if __name__ == '__main__':
>    import sys
>    if len(sys.argv) < 2:
>        print >>sys.stderr, "Usage:", sys.argv[0], "path"
>        sys.exit(1)
>    path = sys.argv[1]
>
>    try:
>        print sort_ls_lf(path)
>    except IOError:
>        pass   # silently absorb broken pipe and other errors
>
> --------------------- cut here ------------------ cut here ------------
>
> Regards,
> -cpghost.
>
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