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SubjectRe: Thinking outside the box on file systems
Date
On Aug 17, 2007, at 15:01:48, Phillip Susi wrote:
> Valdis.Kletnieks@vt.edu wrote:
>> It will become even *more* of a "not that common" if the lock will
>> block moves and ACL changes *across the filesystem* for
>> potentially *minutes* at a time.
>
> It will not take anywhere NEAR minutes at a time to update the in
> memory dentries, more like 50ms.

One last comment:

50ms to update in-memory dentries would be FRIGGING TERRIBLE!!!
Using Perl, an interpreted language, the following script takes 3.39s
to run on one of my lower-end systems:

for (0 .. 10000) {
mkdir "a-$_";
mkdir "b-$_";
rename "a-$_", "b-$_";
}

It's not even deleting things afterwards so it's populating a
directory with ten thousand entries. We can easily calculate
10,000/3.39 = 2,949 entries per second, or 0.339 milliseconds per entry.

When I change it to rmdir things instead, the runtime goes down to
2.89s == 3460 entries/sec == 0.289 milliseconds per entry.

If such a scheme even increases the overhead of a directory rename by
a hundredth of a millisecond on that box it would easily be a 2-3%
performance hit. Given that people tend to kill for 1% performance
boosts, that's not likely to be a good idea.

Cheers,
Kyle Moffett

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