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.

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.


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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