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Date: Thu, 15 May 2008 13:38:55 -0700 (PDT)
From: "stack (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=12597252#action_12597252 ] 

stack commented on HBASE-626:
-----------------------------

On src/java/org/apache/hadoop/hbase/client/MetaScanner.java

+ The class comment could be clearer.  Be explicit it scans the .META. table only (in hbase-speak, up to this, both -ROOT- and .META., are 'meta' tables).
+ FYI, in hadoop, lines are <= 80 characters
+ Why pass in scannerRow and startRow?  When would they ever differ?  Should the opening of the scanner be done with startRow rather than scannerRow since startRow is being updated as we move over regions?

On src/java/org/apache/hadoop/hbase/client/HConnectionManager.java

+ No biggie, but do you think the MetaScanner should return something richer than RowResult? Nearly every Visitor will be doing what your Visitor in this class is doing constructing an HRegionInfo, checking its null.  Should the MetaScanner parse and check for null HRegionInfos returning this plus server and startcodes?

This is patch for all the duplicated code it removes.


> 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
>
>         Attachments: hbase-626-v1.patch
>
>
> 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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