Re: Transaction management in Ozone

Leo Mekenkamp a écrit :
> On Mon, 2004-07-05 at 17:30, Jean Morissette wrote:
> [...]
>>
>>Hi Per,
>>I am interested about the extreme cases that you mentioned about 
>>database corruption.  Could you explain to me when and why such a thing 
>>can happen?  Leo talked previously about ReiserFS4; however I think that 
>>we need to use JNI calls if we want to use transaction functionality 
>>offered by Reiser4, no?
> 
> 
> Applications do not have to be aware of the journalling possibilities of
> a file system to benefit from them. There is fortunately no use
> whatsoever to use JNI.
> 
> Cheers,
> Leo
> 

Here is a note from http://www.namesys.com/
"Full data journaling is considered by many to be a good way to achieve 
file data integrity across system crashes. However, although file data 
may appear to be consistent from the kernel point of view, since there 
is no API exported to the userspace to control transactions, we may 
end-up in a situation where the application makes 2 write requests (as 
part of one logical transaction) but only one of these gets journaled 
before the system crashes. From the application point of view, we may 
then end up with inconsistent data in the file.
Such issues should be addressed with the upcoming ReiserFS v.4 release. 
Such an API will be exported to userspace and all programs that need 
transactions will be able to use it."

So, if we want to use futur ReiserFS v.4 transaction API, we need too 
use JNI, no?

But, the true question is: is-it possible in Java to achieve transaction 
integrity across system crashes (using shadow-paging like Ozone or 
Write-Ahead-Logging like the majority of RDBMS)?  I am concerned about 
Per statement when he says: "some extreme cases such as server power 
failure which under certain unfortunate circumstances can corrupt the
database."  Could you describe the problem please?  Is-there a solution?

Thanks
Jean





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