[Yanel-dev] Fwd: Cluster documentation

[Michael Wechner]

On 2/3/11 7:41 AM, baszero at gmail.com wrote:
> Hoi Michi,
> are your stress tests involving write access?

we are currently working on such tests, whereas one needs to 
differentiate between different cases

Btw, the following Magnolia documentation might also be interesting:

http://documentation.magnolia-cms.com/technical-guide/clustering.html

Cheers

Michael
> Cheers
> Balz
>
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> On 02.02.2011, at 23:20, Michael Wechner<michael.wechner at wyona.com>  wrote:
>
>> On 2/2/11 10:56 PM, Cedric Staub wrote:
>>> On Wed, Feb 02, 2011 at 08:50:09PM +0100, Balz Schreier wrote:
>>>> you got it :-) that's what I tried to explain: read, modify and update must
>>>> be a single atomic operation.
>>> Ok, so now I understand what you're trying to achieve. What I thought
>>> of primarily was making sure that files don't get corrupted,
>> I think our primary concern is that data does not get corrupted and
>> also that if you have write and read at the same time, that the read
>> doesn't get incomplete data.
>>
>> Using checkout/checkin solves the main part of the corruption problem, but
>> the corruption can happen while setting the lock. The chances for
>> this depend on how much the application is used for writing and
>> how modular the data model is and in order to guarantee this in
>> any case one could introduce a "singleton service" for locking (also see below re Amazon S3)
>>
>> The concurrent "write/read incomplete data" problem could be mainly solved
>> by buffering the data, but this would still allow chances when "moving the buffer".
>>
>> Having said the above I think it's a question of time/effort versus chances if the problems
>> from above actually happen. I would argue in many cases the chances are very small
>> (this why we are currently running stress tests to have some real data on this instead of
>> a guts feeling).
>>
>> If we want to really solve this problem properly independent of the repository implementation below,
>> then I think we need to introduce something like a "synchronized singleton service" which can be used
>> by the various cluster apps to get locks.
>>
>> Cheers
>>
>> Michael
>>>   not about
>>> implementing transactions.
>>>
>>> Cedric
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