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From "Karthick Sankarachary (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3777) Redefine Identity Of HBase Configuration
Date Fri, 15 Apr 2011 00:04:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13020118#comment-13020118
] 

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

I changed the assertion in {{TestHCM#testManyNewConneciontsDoesnotOOME}}, moved my test cases
(viz., {{testConnectionSameness}} and {{testConnectionUniqueness}}) there, and verified that
it passes.

About making the {{HConnectionKey#conf}} immutable, the problem is that the user (client)
will still have a reference to the "mutable" instance of the {{Configuration}}, so there's
really no way to enforce its immutability, short of marking the connection properties as "final"
in the hbase-default.xml (but then again, the user can choose to not make it final). In any
case, it's not the end of the world if a connection property were to change after the fact,
because the initial entry for that {{Configuration}} will eventually get evicted, but not
before deleting the {{HConnection}}, so we should be okay.



> 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, 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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