[mysql-dde] Re: Fw: P/F/U Keys in LDD

  • From: "Fabricio Mota" <fabricio.oliveira@xxxxxxxxxxxxxxxx>
  • To: <mysql-dde@xxxxxxxxxxxxx>
  • Date: Thu, 15 Dec 2005 10:04:34 -0200

----- Original Message ----- 
From: "Peter B. Volk" <peter.benjamin.volk@xxxxxxxxxxxxxxxxx>
To: <mysql-dde@xxxxxxxxxxxxx>
Sent: Wednesday, December 14, 2005 9:46 PM
Subject: [mysql-dde] Re: Fw: P/F/U Keys in LDD


>> Well I think we're agreeing in a point: late sync, for the most it is
> used,
>> it must always ensure consistence. What you announced is a *time window
> *of
>> inconsistence.
>>
>> What I would propose for that is: when any operation is performed,
> although
>> a server is down or incommunicable - late-sync targeted or not - no
>> operation targeted to it must be allowed.
>
> Yes Yes give me more.....

What does it mean?

>> The fundamentals of late-sync - in my concept, of course - is that it 
>> must
>> be an passive and *rightless* element of the transaction, unable to 
>> decide
>> if it could be performed or not. If he is an active element (such as:
> delete
>> * from LDDTable where Server = 1 ----- note that here, for example, 
>> Server
> 1
>> is an active element), then late sync is not suitable. This violates the
> *lemma
>> 4 *of late sync.
>
> I fully agree
>
>>
>> Imagine: if in the delete query, there is an foreign key related to any 
>> of
>> these records? If we allow to delete it (with server down), it could be a
>> disaster!
>
> Yes I agree. But once the Delete was executed an found as valid (in terms 
> of
> consistency) on one server (what ever consistency method it uses) then the
> other servers would only need to executed since a server wold have already
> evaluated it.

Yes. only if the down server could not have autonomy to disagree with the 
command independently from the others. If every server could have the same 
behavior in delete command (such as RDD), then late sync could be suitable.
In case of LDD, atempting to delete a record in a down server could not be 
good for late sync.

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