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https://issues.apache.org/jira/browse/HBASE-5399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13217267#comment-13217267
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stack commented on HBASE-5399:
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Ditto w/ zk? Can't we just add close to the HConnection Interface and it will
decrement the ref counting?
> Cut the link between the client and the zookeeper ensemble
> ----------------------------------------------------------
>
> Key: HBASE-5399
> URL: https://issues.apache.org/jira/browse/HBASE-5399
> Project: HBase
> Issue Type: Improvement
> Components: client
> Affects Versions: 0.94.0
> Environment: all
> Reporter: nkeywal
> Assignee: nkeywal
> Priority: Minor
> Attachments: 5399_inprogress.patch, 5399_inprogress.v3.patch,
> 5399_inprogress.v9.patch
>
>
> The link is often considered as an issue, for various reasons. One of them
> being that there is a limit on the number of connection that ZK can manage.
> Stack was suggesting as well to remove the link to master from HConnection.
> There are choices to be made considering the existing API (that we don't want
> to break).
> The first patches I will submit on hadoop-qa should not be committed: they
> are here to show the progress on the direction taken.
> ZooKeeper is used for:
> - public getter, to let the client do whatever he wants, and close ZooKeeper
> when closing the connection => we have to deprecate this but keep it.
> - read get master address to create a master => now done with a temporary
> zookeeper connection
> - read root location => now done with a temporary zookeeper connection, but
> questionable. Used in public function "locateRegion". To be reworked.
> - read cluster id => now done once with a temporary zookeeper connection.
> - check if base done is available => now done once with a zookeeper
> connection given as a parameter
> - isTableDisabled/isTableAvailable => public functions, now done with a
> temporary zookeeper connection.
> - Called internally from HBaseAdmin and HTable
> - getCurrentNrHRS(): public function to get the number of region servers and
> create a pool of thread => now done with a temporary zookeeper connection
> -
> Master is used for:
> - getMaster public getter, as for ZooKeeper => we have to deprecate this but
> keep it.
> - isMasterRunning(): public function, used internally by HMerge & HBaseAdmin
> - getHTableDescriptor*: public functions offering access to the master. =>
> we could make them using a temporary master connection as well.
> Main points are:
> - hbase class for ZooKeeper; ZooKeeperWatcher is really designed for a
> strongly coupled architecture ;-). This can be changed, but requires a lot of
> modifications in these classes (likely adding a class in the middle of the
> hierarchy, something like that). Anyway, non connected client will always be
> really slower, because it's a tcp connection, and establishing a tcp
> connection is slow.
> - having a link between ZK and all the client seems to make sense for some
> Use Cases. However, it won't scale if a TCP connection is required for every
> client
> - if we move the table descriptor part away from the client, we need to find
> a new place for it.
> - we will have the same issue if HBaseAdmin (for both ZK & Master), may be we
> can put a timeout on the connection. That would make the whole system less
> deterministic however.
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