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From Flavio Junqueira <...@yahoo-inc.com>
Subject Re: Concurrent reads and writes on BookKeeper
Date Thu, 20 May 2010 15:42:04 GMT
We have such a mechanism already, as Utkarsh mentions in the jira. The  
question is if we need more sophisticated mechanisms implemented, or  
if we should leave to the application to implement it. For now, we  
haven't felt the need for such extra mechanisms implemented along with  
BK, but I'd certainly be happy to hear a different perspective.

Having said that, we have interesting projects to get folks involved  
with BK, but I don't have it clear that this is one of them.


On May 20, 2010, at 1:36 AM, Patrick Hunt wrote:

> On 05/19/2010 01:23 PM, Flavio Junqueira wrote:
>> Hi Andre, To guarantee that two clients that read from a ledger will
>> read the same sequence of entries, we need to make sure that there is
>> agreement on the end of the sequence. A client is still able to read
>> from an open ledger, though. We have an open jira about informing
>> clients of the progress of an open ledger (ZOOKEEPER-462), but we
>> haven't reached agreement on it yet. Some folks think that it is best
>> that each application use the mechanism it finds best. One option  
>> is to
>> have the writer writing periodically to a ZooKeeper znode to inform  
>> of
>> its progress.
> Hi Flavio. Seems like wrapping up a couple/few of these options in the
> client library (or "a" client library) would be useful for users --
> reuse rather than everyone reinvent. Similar to how we now provide
> recipes in zk source base rather than everyone rewriting the basic
> locks/queues... Would be a great project I would think for someone
> interested in getting started with bk (and to some extent zk)  
> development.
> Patrick
>> I would need to know more detail of your application before  
>> recommending
>> you to stick with BookKeeper or switch to ZooKeeper. If your  
>> workload is
>> dominated by writes, then BookKeeper might be a better option.
>> -Flavio
>> On May 19, 2010, at 1:29 AM, André Oriani wrote:
>>> Sorry, I forgot the subject on my last message :|
>>> Hi all,
>>> I was considering BookKeeper to implement some server replicated
>>> application having one primary server as writer and many backup  
>>> servers
>>> reading from BookKeeper concurrently. The last documentation a I had
>>> access says "This writer has to execute a close ledger operation  
>>> before
>>> any other client can read from it." So readers cannot ready any  
>>> entry on
>>> the ledger, even the already committed ones until writer stops  
>>> writing to
>>> the ledger,i.e, closes it. Is my understanding right ? Should I  
>>> then use
>>> Zookeeper directly to achieve what I want ?
>>> Thanks for the attention,
>>> André Oriani

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