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From "Karthick Sankarachary (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3777) Redefine Identity Of HBase Configuration
Date Wed, 13 Apr 2011 21:42:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13019570#comment-13019570
] 

Karthick Sankarachary commented on HBASE-3777:
----------------------------------------------

Ted, 

I saw your comment on HBASE-3734. It:

a) Proposes a neater way of comparing {{Configuration}} instances, for the purposes of {{HConnection}}
lookup. In fact, the thought of comparing just the cluster-specific properties in {{HBaseConfiguration}}
did cross my mind. However, at times, you may want the ability to have multiple connections
per cluster, which would not be possible using your approach. 

b) Validates the need for having a reference count on the connection. Instead of using a (refcount,
connection) tuple as the value in HBASE_INSTANCES though, HBASE-3766 puts the refcount in
the connection itself. Do you see a specific advantage to separating out the refcount from
the connection?

Regards,
Karthick



> Redefine Identity Of HBase Configuration
> ----------------------------------------
>
>                 Key: HBASE-3777
>                 URL: https://issues.apache.org/jira/browse/HBASE-3777
>             Project: HBase
>          Issue Type: Improvement
>          Components: client, ipc
>    Affects Versions: 0.90.2
>            Reporter: Karthick Sankarachary
>            Assignee: Karthick Sankarachary
>            Priority: Minor
>             Fix For: 0.92.0
>
>         Attachments: HBASE-3777.patch
>
>
> Judging from the javadoc in {{HConnectionManager}}, sharing connections across multiple
clients going to the same cluster is supposedly a good thing. However, the fact that there
is a one-to-one mapping between a configuration and connection instance, kind of works against
that goal. Specifically, when you create {{HTable}} instances using a given {{Configuration}}
instance and a copy thereof, we end up with two distinct {{HConnection}} instances under the
covers. Is this really expected behavior, especially given that the configuration instance
gets cloned a lot?
> Here, I'd like to play devil's advocate and propose that we "deep-compare" {{HBaseConfiguration}}
instances, so that multiple {{HBaseConfiguration}} instances that have the same properties
map to the same {{HConnection}} instance. In case one is "concerned that a single {{HConnection}}
is insufficient for sharing amongst clients",  to quote the javadoc, then one should be able
to mark a given {{HBaseConfiguration}} instance as being "uniquely identifiable".
> Note that "sharing connections makes clean up of {{HConnection}} instances a little awkward",
unless of course, you apply the change described in HBASE-3766.

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