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https://issues.apache.org/jira/browse/HBASE-1287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12689115#action_12689115
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Lars George commented on HBASE-1287:
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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.
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
{code}
public setNumMapTasks(String table, JobConf job) {...}
public setNumReduceTasks(String table, JobConf job) {...}
{code}
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
> {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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