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From Patrick Hunt <ph...@apache.org>
Subject Re: Concurrent reads and writes on BookKeeper
Date Wed, 19 May 2010 23:36:23 GMT

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.


> 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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