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From Dmitry Serebrennikov <dmit...@earthlink.net>
Subject Re: Testcase failure on OSX
Date Tue, 30 Sep 2003 22:37:37 GMT
Hani Suleiman wrote:

> The count for FSDirectory on OSX is around 700-800. The problem is 
> that  the filesystem timestamps on OSX has abysmal resolution (nothing 
> finer  than 1 whole second!) 

Wow! Write once, debug everywhere...
Is this an OSX "feature" or is this a feature of a particular disk / 
filesystem / driver / whatnot that is in use in the current run?
If this is unavoidable on OSX, perhaps other platforms are also 
affected? Does anyone know the timestamp resolution on Wintel, Lintel, 
Solaris, etc?

Finally, what if we allocate a "long" in the beginning of the files that 
need to be touched (like the segments and other files) and use it to 
store the full System.currentTimeMillis timestamp? Does this method 
return a more granular number on OSX? This would be a big change, but it 
would work the same on all platforms and will not have a slowdown.

>
>
> So the touch method will spin its wheels for anything up to a second  
> before we've registered an actual 'touch'.
>
> This isn't so bad as files aren't touch that often, but it's a lot 
> more  problematic in the case of SegmentInfos.write(), where a new 
> file is  created, then copied over the old one. The  
> testDeleteReaderWriteConflict testcase fails due to this. The old 
> file  and the new have the same timestamp, and so the staleness check 
> fails.  How should this be fixed?
>
> Also, won't the fix for FSDirectory mean there's a window where other  
> threads could end up with bad info, if we're taking up to a second to  
> touch a file?

I don't know off hand, but I believe there is file locking in place to 
prevent other threads from getting into this code until the update 
operation is completed, and it will not be completed until the touch 
finishes. This still sucks with a 1-second blocking...

Dmitry.



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