解决sqoop报错：java.lang.OutOfMemoryError: Java heap space

报错栈：

-- ::, INFO [main] org.apache.sqoop.mapreduce.db.DBRecordReader: Executing query: select "CTJX60","CTJX61","CTJX62","CTJX63","CTJX64","CTJX65","CTJX66","CTJX67","CTJX68","CTJX69","CTJX70","CTJX71","CTJX72","CTJX73","CTJX74","CTJX75","CTJX76","CTJX77","CTJX78","CTJX79","CTJX80","CTJX81","CTJX82","CTJX83","CTJX84","CTJX85","CTJX86","CTJX87","CTJX88","CTJX89","CTJX90","CTJX91","CTJX92","CTJX93","CTJX94","CTJX95","CTJX96","CTJX97","CTJX98","CTJX99","CTJX55","IID","IEXAM_IID","CTSBGLX","CTJX01","CTJX02","CTJX03","CTJX04","CTJX05","CTJX06","CTJX07","CTJX08","CTJX09","CTJX10","CTJX11","CTJX12","CTJX13","CTJX14","CTJX15","CTJX16","CTJX17","CTJX18","CTJX19","CTJX20","CTJX21","CTJX22","CTJX23","CTJX24","CTJX25","CTJX26","CTJX27","CTJX28","CTJX29","CTJX30","CTJX31","CTJX32","CTJX33","CTJX34","CTJX35","CTJX36","CTJX37","CTJX38","CTJX39","CTJX40","CTJX41","CTJX42","CTJX43","CTJX44","CTJX45","CTJX46","CTJX47","CTJX48","CTJX49","CTJX50","CTJX51","CTJX52","CTJX53","CTJX54","CTJX56","CTJX57","CTJX58","CTJX59" from RIS."ICNRIS_UIS_EXAM_TJX" tbl where ( = ) AND ( = )
-- ::, INFO [Thread-] org.apache.sqoop.mapreduce.AutoProgressMapper: Auto-progress thread is finished. keepGoing=false
-- ::, FATAL [main] org.apache.hadoop.mapred.YarnChild: Error running child : java.lang.OutOfMemoryError: Java heap space
    at oracle.jdbc.driver.OracleStatement.prepareAccessors(OracleStatement.java:)
    at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(OracleStatement.java:)
    at oracle.jdbc.driver.T4CPreparedStatement.executeMaybeDescribe(T4CPreparedStatement.java:)
    at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:)
    at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:)
    at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:)
    at org.apache.sqoop.mapreduce.db.DBRecordReader.executeQuery(DBRecordReader.java:)
    at org.apache.sqoop.mapreduce.db.DBRecordReader.nextKeyValue(DBRecordReader.java:)
    at org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:)
    at org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue(MapContextImpl.java:)
    at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue(WrappedMapper.java:)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:)
    at org.apache.sqoop.mapreduce.AutoProgressMapper.run(AutoProgressMapper.java:)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:)
    at org.apache.hadoop.mapred.YarnChild$.run(YarnChild.java:)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:)

解决：调小sqoop参数：--fetch-size

解决过程，查看sqoop源码，看到fetchSize，想到调整这个参数：

ps: 调大mapper参数不管用，曾设置过参数：-D mapreduce.map.memory.mb=8192 -D yarn.app.mapreduce.am.resource.mb=6144。问题是在从db fetch数据的时候出现的，原表的列不算多，但每个列的长度很大：