Messages in this thread | | | From | Kyle Moffett <> | Subject | Re: Thinking outside the box on file systems | Date | Sat, 18 Aug 2007 01:48:02 -0400 |
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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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