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https://issues.apache.org/jira/browse/HBASE-5139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13191261#comment-13191261
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Hadoop QA commented on HBASE-5139:
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-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12511514/5139.addendum
against trunk revision .
+1 @author. The patch does not contain any @author tags.
-1 tests included. The patch doesn't appear to include any new or modified
tests.
Please justify why no new tests are needed for this
patch.
Also please list what manual steps were performed to
verify this patch.
-1 patch. The patch command could not apply the patch.
Console output: https://builds.apache.org/job/PreCommit-HBASE-Build/836//console
This message is automatically generated.
> Compute (weighted) median using AggregateProtocol
> -------------------------------------------------
>
> Key: HBASE-5139
> URL: https://issues.apache.org/jira/browse/HBASE-5139
> Project: HBase
> Issue Type: Sub-task
> Reporter: Zhihong Yu
> Assignee: Zhihong Yu
> Attachments: 5139-v2.txt, 5139.addendum
>
>
> Suppose cf:cq1 stores numeric values and optionally cf:cq2 stores weights.
> This task finds out the median value among the values of cf:cq1 (See
> http://www.stat.ucl.ac.be/ISdidactique/Rhelp/library/R.basic/html/weighted.median.html)
> This can be done in two passes.
> The first pass utilizes AggregateProtocol where the following tuple is
> returned from each region:
> (partial-sum-of-values, partial-sum-of-weights)
> The start rowkey (supplied by coprocessor framework) would be used to sort
> the tuples. This way we can determine which region (called R) contains the
> (weighted) median. partial-sum-of-weights can be 0 if unweighted median is
> sought
> The second pass involves scanning the table, beginning with startrow of
> region R and computing partial (weighted) sum until the threshold of S/2 is
> crossed. The (weighted) median is returned.
> However, this approach wouldn't work if there is mutation in the underlying
> table between pass one and pass two.
> In that case, sequential scanning seems to be the solution which is slower
> than the above approach.
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