On Thu, 29 Nov 2007 08:42:44 -0500
Bill Moran <[EMAIL PROTECTED]> wrote:
> In response to Wojciech Puchar <[EMAIL PROTECTED]>:
>
> > > ls | wc
> >
> > strange. i did
> >
> > [EMAIL PROTECTED] ~/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.
--
Cordula's Web. http://www.cordula.ws/
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