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From Patrick Hunt <ph...@apache.org>
Subject Re: Concurrent reads and writes on BookKeeper
Date Thu, 20 May 2010 22:24:54 GMT

On 05/20/2010 08:42 AM, Flavio Junqueira wrote:
> 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.

Ok, was just saying that we shouldn't be too strict about it (impls 
available "out of the box"). Otw we run into situations similar to zk 
recipes where multiple users were re-implementing common patterns.

> 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.

It would be great if you could enter JIRAs on this (projects), perhaps 
also a wiki 'interesting projects around bk (or hedwig, etc...)' page 
that catalogs those JIRAs.



> -Flavio
> 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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