Re: Was able to reproduce "cp: cannot stat file.x: Input/output error"

[Hans Reiser <reiser@namesys.com>]

Alex Zarochentsev wrote:

>On Tue, Aug 10, 2004 at 10:35:58AM -0700, Hans Reiser wrote:
>  
>
>>Alex Zarochentsev wrote:
>>
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>>>On Mon, Aug 09, 2004 at 11:21:17PM -0400, Valdis.Kletnieks@vt.edu wrote:
>>>
>>>
>>>      
>>>
>>>>On Sat, 07 Aug 2004 00:49:43 PDT, Hans Reiser said:
>>>>
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>>>>
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>>>>
>>>>>>I think I have discovered the problem - unless there was a reason mongo 
>>>>>>was
>>>>>>issuing mount/unmount commands at the start/end of a mongo 'run' as 
>>>>>>well as
>>>>>>before/after _each phase_.
>>>>>>      
>>>>>>
>>>>>>            
>>>>>>
>>>>>Probably someone wanted to separate the measurement of the phases.  It 
>>>>>has been a while since I read mongo.....
>>>>>    
>>>>>
>>>>>          
>>>>>
>>>>Note that an unmount/mount pair will force a flush of all dirtied pages 
>>>>in the
>>>>in-memory file cache, and *really* not return until it's really done and 
>>>>really
>>>>out on disk.  In addition, sync() will force stuff to disk, but *not* 
>>>>invalidate
>>>>in-cache pages - more drastic measures are needed if you want to benchmark
>>>>with a cold cache (which is almost a must if you're doing actual 
>>>>filesystem
>>>>benchmarking, as otherwise you're benching the in-core cache instead).
>>>>  
>>>>
>>>>        
>>>>
>>>That was designed to have result in each phase as independent as we can.  
>>>For
>>>example, if we have read slowdown in mongo, we will analyze only reads and,
>>>probably, fs fragmentation, we won't deal with unmeasurable cache state 
>>>before
>>>the read phase. Known and persistent "cold cache effect" is better than 
>>>unknown
>>>hot cache one :)  And, mongo phases are designed to be long and keep the 
>>>cold
>>>cache effect at minimum.
>>>
>>>
>>>      
>>>
>>Let me be more precise here.  Is the time spent mounting and umounting 
>>included in the time for the phase?
>>    
>>
>
>oops. sync time included. mount/umount time is not.
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You see the problem, yes?  Your suggestion?