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From "Lars George (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1287) Partitioner class not used in TableMapReduceUtil.initTableReduceJob()
Date Wed, 25 Mar 2009 14:00:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12689115#action_12689115

Lars George commented on HBASE-1287:

I was wondering about this too Michael and was about to ask. I am not sure who added it and
why (I have yet to figure out how to search the file history for a specific change as opposed
to browse them one by one). Anyhow, I do a similar thing, computing the number of mappers,
in my main MR program. Why this is here and why it is executed just when a custom partitioner
is given eludes me. Either you do it always, or never - or have an extra flag that triggers

It also sets the upper limit only when the given number of reducers is higher than the actual
regions. Why though? I am using this only to compute the number of mappers so that I do not
have to specify this on the command line. 

All in all I would drop the whole thing if there is no reason to keep it and rather ask the
caller to set the boundaries. Or add another helper method that computes these on demand,
for example

public setNumMapTasks(String table, JobConf job) {...}
public setNumReduceTasks(String table, JobConf job) {...}

where both simply do the same thing, get the number of region and assign that value to the
respective field in the job configuration.

> Partitioner class not used in TableMapReduceUtil.initTableReduceJob()
> ---------------------------------------------------------------------
>                 Key: HBASE-1287
>                 URL: https://issues.apache.org/jira/browse/HBASE-1287
>             Project: Hadoop HBase
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Lars George
>            Assignee: Lars George
>         Attachments: 1287.patch
> Upon checking the available utility methods in TableMapReduceUtil I came across this
> {code}
>   public static void initTableReduceJob(String table,
>     Class<? extends TableReduce> reducer, JobConf job, Class partitioner)
>   throws IOException {
>     job.setOutputFormat(TableOutputFormat.class);
>     job.setReducerClass(reducer);
>     job.set(TableOutputFormat.OUTPUT_TABLE, table);
>     job.setOutputKeyClass(ImmutableBytesWritable.class);
>     job.setOutputValueClass(BatchUpdate.class);
>     if (partitioner != null) {
>       job.setPartitionerClass(HRegionPartitioner.class);
>       HTable outputTable = new HTable(new HBaseConfiguration(job), table);
>       int regions = outputTable.getRegionsInfo().size();
>       if (job.getNumReduceTasks() > regions){
>     	job.setNumReduceTasks(outputTable.getRegionsInfo().size());
>       }
>     }
>   }
> {code}
> It seems though as it should be
> {code}
>     if (partitioner != null) {
>       job.setPartitionerClass(partitioner);
> {code}
> and the provided HRegionPartitioner can be handed in to that call or a custom one can
be provided.

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