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POHadoop conf to determine num map tasks
 

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    <p>I have a job, like all my Hadoop jobs, it seems to have a total of 2 map tasks when running from what I can see in the Hadoop interface. However, this means it is loading so much data that I get a Java Heap Space error.</p> <p>I've tried setting many different conf properties in my Hadoop cluster to make the job split into more tasks but nothing seems to have any effect.</p> <p>I have tried setting <code>mapreduce.input.fileinputformat.split.maxsize</code>, <code>mapred.max.split.size</code>, <code>dfs.block.size</code> but none seem to have any effect.</p> <p>I'm using 0.20.2-cdh3u6, and trying to run a job using cascading.jdbc - the job is failing on reading data from the database. I think this issue can be resolved by increasing the number of splits but can't work out how to do that! </p> <p>Please help! Going crazy!</p> <pre><code>2013-07-23 09:12:15,747 FATAL org.apache.hadoop.mapred.Child: Error running child : java.lang.OutOfMemoryError: Java heap space at com.mysql.jdbc.Buffer.&lt;init&gt;(Buffer.java:59) at com.mysql.jdbc.MysqlIO.nextRow(MysqlIO.java:1477) at com.mysql.jdbc.MysqlIO.readSingleRowSet(MysqlIO.java:2936) at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:477) at com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:2631) at com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:1800) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2221) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2618) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2568) at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1557) at cascading.jdbc.db.DBInputFormat$DBRecordReader.&lt;init&gt;(DBInputFormat.java:97) at cascading.jdbc.db.DBInputFormat.getRecordReader(DBInputFormat.java:376) at cascading.tap.hadoop.MultiInputFormat$1.operate(MultiInputFormat.java:282) at cascading.tap.hadoop.MultiInputFormat$1.operate(MultiInputFormat.java:277) at cascading.util.Util.retry(Util.java:624) at cascading.tap.hadoop.MultiInputFormat.getRecordReader(MultiInputFormat.java:276) at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:370) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:324) at org.apache.hadoop.mapred.Child$4.run(Child.java:266) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:415) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1278) at org.apache.hadoop.mapred.Child.main(Child.java:260) </code></pre>
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    1. USKatie
    1. USKatie
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      1. VTUpMod
    1. COWould you mind sharing some code of what you are doing inside your map() function?
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      1. USSSaikia_JtheRocker
    2. COCan you describe the source for the data? Are you pulling from a database, or from the filesystem? If the latter, what is the file type?
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      1. USmohit6up
    3. COI'm pulling from a database table, one Tap source is 637,018 rows, the other is 116,198 rows. The job fails before it reaches any cascading functions I've written myself. I'll add the exception to my question.
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      1. USKatie
 

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