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From "nkeywal (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5399) Cut the link between the client and the zookeeper ensemble
Date Tue, 06 Mar 2012 20:59:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13223657#comment-13223657

nkeywal commented on HBASE-5399:

@all; Ok, I will provide an updated patch with the comments taken into account. I also understood
the issue behind TestZooKeeper. My fix currently breaks other unit tests, but if I manage
to make it work I will include it.

For 0.94 vs. 0.96 ok as well, however, it would makes sense to deprecate some methods in the
0.94, especially getMaster & getZooKeeper in HConnection: people will get more time to
react this way.
> 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
>             Fix For: 0.96.0
>         Attachments: 5399.v27.patch, 5399.v38.patch, 5399.v39.patch, 5399.v40.patch,
5399_inprogress.patch, 5399_inprogress.v14.patch, 5399_inprogress.v16.patch, 5399_inprogress.v18.patch,
5399_inprogress.v20.patch, 5399_inprogress.v21.patch, 5399_inprogress.v23.patch, 5399_inprogress.v3.patch,
5399_inprogress.v32.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
> - 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
> - 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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