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From Adam Kocoloski <kocol...@apache.org>
Subject Re: Data loss
Date Sat, 07 Aug 2010 23:58:53 GMT
I believe it's a single delayed conflict write attempt and no successes in that same interval.

On Aug 7, 2010, at 7:51 PM, Damien Katz wrote:

> Looks like all that's necessary is a single delayed conflict write attempt, and all subsequent
delayed commits won't be commit, the header never gets written.
> 
> 1.0 loses data. This is ridiculously bad.
> 
> We need a test to reproduce this and fix.
> 
> -Damien
> 
> On Aug 7, 2010, at 4:35 PM, Adam Kocoloski wrote:
> 
>> Good sleuthing guys, and my apologies for letting this through.  Randall, your patch
in COUCHDB-794 was actually fine, it was my reworking of it that caused this serious bug.
>> 
>> With respect to that gist 513282, I think it would be better to return Db#db{waiting_delayed_commit=nil}
when the headers match instead of moving the cancel_timer() command as you did.  After all,
we did perform the check here -- it was just that nothing needed to be committed.
>> 
>> Adam
>> 
>> On Aug 7, 2010, at 6:55 PM, Damien Katz wrote:
>> 
>>> Yes, I think it requires 2 conflicting writes in row, because it needs to trigger
the delayed_commit timer without actually having anything to commit, so the header never changes.
>>> 
>>> Try to reproduce this and add a test case.
>>> 
>>> -Damien
>>> 
>>> 
>>> On Aug 7, 2010, at 3:47 PM, Randall Leeds wrote:
>>> 
>>>> I think you may be right, Damien.
>>>> If ever a write happens that only contains conflicts while waiting for
>>>> a delayed commit message we might still be cancelling the timer. Is
>>>> this what you're thinking? This would be the fix:
>>>> http://gist.github.com/513282
>>>> 
>>>> On Sat, Aug 7, 2010 at 15:42, Damien Katz <damien@apache.org> wrote:
>>>>> I think the problem might be that 2 conflicting write attempts in row
can leave the #db.waiting_delayed_commit set but the timer has been cancelled. One that happens,
the header may never be written, as it always thinks a delayed commit will fire soon.
>>>>> 
>>>>> -Damien
>>>>> 
>>>>> 
>>>>> On Aug 7, 2010, at 12:08 PM, Randall Leeds wrote:
>>>>> 
>>>>>> On Sat, Aug 7, 2010 at 11:56, Randall Leeds <randall.leeds@gmail.com>
wrote:
>>>>>>> I agree completely! I immediately thought of this because I wrote
that
>>>>>>> change. I spent a while staring at it last night but still can't
>>>>>>> imagine how it's a problem.
>>>>>>> 
>>>>>>> On Sat, Aug 7, 2010 at 11:12, Damien Katz <damien@apache.org>
wrote:
>>>>>>>> SVN commit r954043 looks suspicious. Digging further.
>>>>>>>> 
>>>>>>>> -Damien
>>>>>>> 
>>>>>> 
>>>>>> I still want to stare at r954043, but it looks to me like there's
at
>>>>>> least one situation where we do not commit data correctly during
>>>>>> compaction. This has to do with the way we now use the path to sync
>>>>>> outside the couch_file:process. Check this diff:
>>>>>> http://gist.github.com/513081
>>>>> 
>>>>> 
>>> 
>> 
> 


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