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LWN.net Weekly Edition for May 23, 2013
An "enum" for Python 3
An unexpected perf feature
LWN.net Weekly Edition for May 16, 2013
A look at the PyPy 2.0 release
Posted Dec 31, 2010 16:21 UTC (Fri) by man_ls (subscriber, #15091)
Posted Dec 31, 2010 19:05 UTC (Fri) by etienne (subscriber, #25256)
Well, for decades you did not have hard drives with internal command queueing.
To have better performances you need to keep the queue full.
Because you cannot tell the hard drive that updating this sector is more important than that one, that information is probably not managed at all in the driver.
Moreover, you asked for this behaviour by wanting only metadata journaling of the filesystem, explicitely wanting a coherant filesystem (i.e. no fsck after crash) even if it means data inside files may be corrupted.
You can run with data journaling, but people/distributions thinks it does not worth the performance hit.
Once again, reenacting history
Posted Dec 31, 2010 20:21 UTC (Fri) by man_ls (subscriber, #15091)
The funny thing is that XFS developers eventually realized their folly and solved the atomicity issues, but now people don't trust them with their data anymore.
Posted Dec 31, 2010 22:14 UTC (Fri) by neilbrown (subscriber, #359)
which can easily leave nothing called "file". This is all that "atomic rename" means, or at least all it meant before ext3 gave rename unfortunate (though useful) semantics.
Though I cannot know the intention of the author of that post you linked to, there is no prima-face reason to believe they mean anything more than the atomicity of names (not of contents) that rename has always had in Unix.
(and half-written files are easy to detect by writing a checksum at the end. If you suffix each file with a timestamp it is easy to know which is the most recent. And file older than a few minutes will be safe-on-disk so you are always free to clean up any file older than the youngest file that is older than a few minutes)
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