Eric Anderson wrote:
Mark Bucciarelli wrote:
On Sat, Feb 18, 2006 at 11:06:57PM -0500, Mark Bucciarelli wrote:
I'm curious how fast stat is.
I generated a list of 200,000 file names
# find / | head -200000 > files.statspeed
then ran a million iterations of randomly picking a file name and
stating it (see attached program).
Hmmm, 200,000 files 1,000,000 iterations. On avg, each file hit
five times. Uhh, that's not a good way to avoid caching. Doh.
Wow, caching is pretty amazing. I just reran the program, this time
using 500,000 file paths and only stat'ing 10,000 of them.
The first run was 99,059/second, the second was 188,239.
So I guess 100,000/second is about right on my system w/o cache.
I'm also wondering if by using find, and getting a list of
files/directories in the default order, you might be seeing some
results that aren't really completely random. What I mean is, your
find is traversing the tree, probably digging through directories
based on inode number or last modified time (can't recall which), but
either way, it's possible your list consisted of clumps of files/dirs
in the same cylinder groups, specially since you grabbed the first
500k files, instead of picking a random file from the entire list of
files on the filesystem, and building a list from that random
plucking.. This is all speculative, but if you had lots of files in a
directory, those could be clumped in a few cylinder groups and
therefore you might see higher numbers than sampling from the entire
disk (since the speed is probably mostly dominated by disk seeks I
believe).
What exactly are you trying to determine?
You are also timing the rand() function. I suggest randomizing the list
first, then stating the files in the randomized list.
Eric
--
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Eric Anderson Sr. Systems Administrator Centaur Technology
Anything that works is better than anything that doesn't.
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