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https://issues.apache.org/jira/browse/HBASE-2965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12990891#comment-12990891
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Akash Ashok commented on HBASE-2965:
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Hi, I was lookin for the exact same thing. As we are moving from just
processing on hadoop to using Hbase, we are in dire need of this
MultipleTableInputs for our reduce side joins. Could some1 please temme as to
when this will be implemented .
Also can I move this feature from Minor to Major as this is a very important
feature?
> Implement MultipleTableInputs which is analogous to MultipleInputs in Hadoop
> ----------------------------------------------------------------------------
>
> Key: HBASE-2965
> URL: https://issues.apache.org/jira/browse/HBASE-2965
> Project: HBase
> Issue Type: New Feature
> Components: mapred, mapreduce
> Reporter: Adam Warrington
> Priority: Minor
>
> This feature would be helpful for doing reduce side joins, or even passing
> similarly structured data from multiple tables through map reduce. The API I
> envision would be very similar to the already existent MultipleInputs, parts
> of which could be reused.
> MultipleTableInputs would have a public api like:
> class MultipleTableInputs {
> public static void addInputTable(Job job, Table table, Scan scan, Class<?
> extends TableInputFormatBase> inputFormatClass, Class<? extends Mapper>
> mapperClass);
> };
> MultipleTableInputs would build a mapping of Tables to configured
> TableInputFormats the same way MultipleInputs builds a mapping between Paths
> and InputFormats. Since most people will probably use TableInputFormat.class
> as the input format class, the MultipleTableInput implementation will have to
> replace the TableInputFormatBase's private scan and table members that are
> configured when an instance of TableInputFormat is created (from within its
> setConf() method) by calling setScan and setHTable with the table and scan
> that are passed into addInputTable above. MultipleTableInputFormat's
> addInputTable() member function would also set the input format for the job
> to DelegatingTableInputFormat, described below.
> A new class called DelegatingTableInputFormat would be analogous to
> DelegatingInputFormat, where getSplits() would return TaggedInputSplits (same
> TaggedInputSplit object that the Hadoop DelegatingInputFormat uses), which
> tag the split with its InputFormat and Mapper. These are created by looping
> through the HTable to InputFormat mappings, and calling getSplits on each
> input format, and using the split, the input format, and mapper as
> constructor args to TaggedInputSplits.
> The createRecordReader() function in DelegatingTableInputFormat could have
> the same implementation as the Hadoop DelegatingInputFormat.
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