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Re: [jgit-dev] File timestamp precision on Linux
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11 nov 2010 kl. 00:08 skrev Matthias Sohn:
> 2010/11/10 Lluis Sanchez Gual <slluis.devel@xxxxxxxxx>
>
>> Hi,
>>
>> In WorkingTreeIterator.isModified there is some code for rounding cached
>> timestamps to seconds, since Java on Windows gives times with a
>> precision of seconds. However, I'm noticing a similar issue on Linux.
>>
>> Java on Linux is returning times rounded to seconds. The problem is that
>> the C git stores timestamps using millisecond precision. So for example,
>> if I run "git reset --hard" and then traverse the working tree using a
>> TreeWalk checking isModified for each item, the date comparison will
>> almost always fail (milliseconds won't match), leading to many full
>> content checks, which is much slower.
>>
>> This issue can be solved in WorkingTreeIterator by rounding the cached
>> timestamp to seconds when the last write time of the file being checked
>> is also rounded to seconds. However, I'm wondering if this is a known
>> issue that it is handled in a different way in other places of the code.
>>
>
> AFAIK there are some filesystem rounding timestamps to seconds, according
> to
> [1] Java is returning timestamps with ms precision (though not nsec).
>
> E.g. ext3, hfs+ round timestamps to seconds [2], whereas ext4, xfs,
> jfs provide
> nsec resolution [3].
Unfortunately Java truncates the timestamp on Linux [5]. I've
noticed it with XFS, so I think the problem is file system agnostic.
> On Windows ntfs provides 100 nsec resolution.
GitIndex had some rounding, that assumed that if a timestamp has 0 in the millisecond
part, it would truncate the timestamp it compared with to whole seconds.
> Combining this information I am not yet sure what's the right approach here.
>
> [1]
> http://download.oracle.com/javase/6/docs/api/java/io/File.html#lastModified()
> [2] http://en.wikipedia.org/wiki/Ext3, http://en.wikipedia.org/wiki/HFS_Plus
> [3] http://en.wikipedia.org/wiki/Ext4
> [4] http://en.wikipedia.org/wiki/NTFS
[5] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6939260
-- robin
