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https://issues.apache.org/jira/browse/ZOOKEEPER-373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12699341#action_12699341
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Flavio Paiva Junqueira commented on ZOOKEEPER-373:
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With this patch, a BookKeeper client has only one BookieHandle per Bookie. With 
the current trunk implementation, if a client creates writes to two ledgers 
simultaneously and they share a bookie, there will be two BookieHandle threads. 
This is not a problem for applications like the namenode that writes to one 
ledger at a time, but there might be applications that require clients writing 
to several ledgers concurrently. 

More specifically, with this patch, a BookKeeper object keeps a list of 
BookieHandle objects. When creating a ledger, LedgerHandle checks if there is a 
BookieHandle object available before instantiating BookieHandle through a call 
to BookKeeper::getBookieHandle. We then have to make sure that a BookieHandle 
keeps running as long as there is at least one reference to it. 

  

> One thread per bookie
> ---------------------
>
>                 Key: ZOOKEEPER-373
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-373
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: contrib-bookkeeper
>    Affects Versions: 3.1.1
>            Reporter: Flavio Paiva Junqueira
>            Assignee: Flavio Paiva Junqueira
>             Fix For: 3.2.0
>
>         Attachments: ZOOKEEPER-373.patch, ZOOKEEPER-373.patch
>
>
> Currently, if a client is writing to multiple ledgers and these ledgers 
> overlap on some bookie, there will be as many threads for such a bookie as 
> the number of ledgers writing to it. Consequently, if a client writes to many 
> ledgers simultaneously, it may end up with an undesirably large number of 
> threads. I don't have a concrete proposal yet, but I suspect it is as simple 
> as keeping an array of BookieHandle objects, one per bookie, and having each 
> BookieHandle object shared by all ledgers.
>  

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