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From "stack (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5399) Cut the link between the client and the zookeeper ensemble
Date Fri, 17 Feb 2012 22:22:57 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13210616#comment-13210616
] 

stack commented on HBASE-5399:
------------------------------

I don't follow:

{code}
+    // todo stack nkeywal
+    // We used to check in a loop that the master was running.
+    // 1) There were imbricated "tries" loop. One here and one in getMaster
+    // 2) As the master can disappear, it may not be necessary to check it.
+    // We don't need the connection immediately, but we used to check the
+    //  connection at the beginning in the past, and it's more user friendly
+    //  to have the error immediately.
+    // connection.isMasterRunning();
{code}

I'd say lets not check master is there till we need it.  Seems like a PITA going ahead and
checking master on construction.  This changes the behavior but I think its one thats ok to
change.

You are doing your own Callables.  You've seen the Callables that go on in HTable.  Any reason
you avoid them?  I suppose this is different in that you want to let go of the shared master.
 Looks fine.

Are we getting retrieveClusterId on startup?  Can we not do that?  Can we do that when someone
asks for it? Or is it happening after we've set up the zk connection anyways?

Patch makes sense so far.  Good stuff N.












                
> 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
>
>
> 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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