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Date: Wed, 14 May 2008 10:26:56 -0700 (PDT)
From: "Jean-Daniel Cryans (JIRA)" <jira@apache.org>
To: hbase-dev@hadoop.apache.org
Subject: [jira] Commented: (HBASE-626) Use Visitor pattern in MetaRegion to
 reduce code clones in HTable and HConnectionManager
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    [ https://issues.apache.org/jira/browse/HBASE-626?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12596838#action_12596838 ] 

Jean-Daniel Cryans commented on HBASE-626:
------------------------------------------

Well in fact I checked this and this is already uses a form of visitor. The listener (usually called observer) reacts to events, which is not the case in this piece of code. But this is the good place I think to do the modification. What I plan is :

- Refactor the scanMetaRegion method so it uses RowResult.
- Modify the listener (renamed visitor) so it accepts a RowResult and a HRegionInfo.
- Add a method to scan all the meta regions which will take a visitor in argument and optionally a row start key.
- Modify all impacted code.

Question : In the TODO it says that it has to "Allow multiple Visitors". Since the ScannerListener already has to be implemented, I don't see the purpose of that comment. Am I missing something bigger?

> Use Visitor pattern in MetaRegion to reduce code clones in HTable and HConnectionManager
> ----------------------------------------------------------------------------------------
>
>                 Key: HBASE-626
>                 URL: https://issues.apache.org/jira/browse/HBASE-626
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: master
>            Reporter: Jean-Daniel Cryans
>            Priority: Minor
>             Fix For: 0.2.0
>
>
> HTable and HConnectionManager.TableServers both scan the meta region in the same way (but the later also retry one time if it fails). A Visitor pattern should be used in a new scanning method in MetaRegion to accept visitors that gather information such as region names for a table or the list of all tables.

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