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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-626) Use Visitor pattern in MetaRegion to reduce code clones in HTable and HConnectionManager
Date Thu, 15 May 2008 20:38:55 GMT

    [ 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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