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https://issues.apache.org/jira/browse/HBASE-5399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13211313#comment-13211313
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nkeywal commented on HBASE-5399:
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bq. 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?
We're doing it when we create the connection, so we're connection for ZK just
for this today. However, I think that we should also connect to ZK to get the
master address (this would allow to start a client without specifying the
master address: today it must be in ZK but also in client configuration). Wet
would still connect to ZK at starting time, so, but for two reasons instead of
only one.
On another hand, There's a comment from Gary on the bug review tracker
(https://review.cloudera.org//r/1669/) for HBASE-3677:
??Yes, no real need for a tracker. Andy and I had discussed that previously.
ZK is just used to broadcast the ID to clients and servers without the need for
HBase RPC (which for token authentication requires selection of the right
token, but we don't know the token without the ID...). I'll post an update
that just reads the ID from ZK without using a tracker.??
So It seems that we could safely:
- remove the clusterIdWatcher class
- replace the conf parameter "hbase.cluster.id" by a simple getter on
Connection. That would allow to get the id only when asked, with a lazy
initialization, hence connecting later to ZK.
I don't mind doing this, but it's better to do it in another jira (this one's
too big already).
> 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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