Re: Transaction management in Ozone

On Wed, 2004-07-07 at 12:55, Per Nyfelt wrote:
> I think your idea is not bad. The big issue as I see it is not that we might 
> loose some data if a system crash occurs in the midst of a transaction but 
> that under certain circumstances we can actually corrupt the database and are 
> forced to rely on backup to recover. I cant remember who it was that did some 
> testing on this and reported the issue initially but it should be in the mail 
> archive somewhere. Anyways, your idea would minimize this risk of corruption 
> right?

As far as I can see it, it would bring risk of corruption to null
percent on this issue; no dataloss nor db corruption. All we need is
someone with enough time to implement it ;-)

By the way, data loss is on the same 'scale of badness' as data
corruption; data loss means you do not know what data has been lost, is
not in sync with the real world anymore, rendering all data worthless;
with data corruption you loose all data, thus rendering all data
worthless. Some even argue that corruption is better than data loss,
since one is more likely to notice corrupted data.

> When it comes to the discussion of how to be 100% certain data is written then 
> the only way I know is to write our own filesystem or hook into the API of a 
> filesystem with the necessary features. But this is outside the scope of the 
> Ozone project IMO since it breaks platform independence. 

Could not agree with you more. As I mentioned in the other email, I do
believe that once a FileOutputStream has closed that the contents are
guaranteed to have been fully flushed to disk. It would be difficult to
see why Sun would go through trouble to ensure 'correct' and cross
platform floating point operations and at the same time not implement
safe file i/o.

Cheers,
Leo




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