Hi,

For option 1: I can not add jars in our cluster as no permission. And we also want to keep our cluster clean and stable.

For option 2:  It does not work as the jars from "-libjar" are not loaded in the client process. 

However, an optional solution is adding my jar to HADOOP_CLASSPATH. 

But here I want to know is why does DBConfiguration not use "conf.getClassByName" to load the jdbc driver?

2013/4/19 vasanth kumar <rj.vasanthkumar@gmail.com>
Hi,

No need to pack mysql packages into your jar.
Option 1: Copy mysql jdbc jar into $HADOOP_HOME/lib. Restart hadoop daemons.

Option 2: while executing try : $hadoop jar your.jar a.b.c.Main -libjar /path/mysql.jar


On Fri, Apr 19, 2013 at 12:32 PM, Shixiong Zhu <zsxwing@gmail.com> wrote:
Hi,

I encountered a ClassNotFoundException when I used DBInputFormat. I packaged my codes with mysql-connector-java-5.1.24.jar to abc.jar. Then I run the following command to run:

hadoop jar abc.jar a.b.c.Main

But it is crashed by the following exception:

  Notes: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.hadoop.mapreduce.lib.db.DBInputFormat.setConf(DBInputFormat.java:158)
at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:70)
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:130)
at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:959)
at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:979)
at org.apache.hadoop.mapred.JobClient.access$500(JobClient.java:170)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:891)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:844)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:416)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1232)
at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:844)
at org.apache.hadoop.mapreduce.Job.submit(Job.java:481)
at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:511)
...
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
at com.microstrategy.etl.alert.feedback.FeedbackDumpTask.main(FeedbackDumpTask.java:17)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.hadoop.util.RunJar.main(RunJar.java:208)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.hadoop.mapreduce.lib.db.DBInputFormat.getConnection(DBInputFormat.java:184)
at org.apache.hadoop.mapreduce.lib.db.DBInputFormat.setConf(DBInputFormat.java:152)
... 25 more
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:186)
at org.apache.hadoop.mapreduce.lib.db.DBConfiguration.getConnection(DBConfiguration.java:143)
at org.apache.hadoop.mapreduce.lib.db.DBInputFormat.getConnection(DBInputFormat.java:178)
... 26 more

I read the DBConfiguration.java file, and found it uses "Class.forName" to load "com.mysql.jdbc.Driver":

   /** Returns a connection object to the DB.
   * @throws ClassNotFoundException
   * @throws SQLException */
  public Connection getConnection()
      throws ClassNotFoundException, SQLException {
    Connection connection;

    Class.forName(conf.get(DBConfiguration.DRIVER_CLASS_PROPERTY));

I think that's why my application crashed. The classloader of DBConfiguration is sun.misc.Launcher$AppClassLoader, but "com.mysql.jdbc.Driver" exists in the URLClassLoader created by org.apache.hadoop.util.RunJar.
So "Class.forName" invoked by DBConfiguration can not find "com.mysql.jdbc.Driver" in the sun.misc.Launcher$AppClassLoader.

Why does DBConfiguration not use "conf.getClassByName" to load the jdbc driver? If DBConfiguration use the following code, it can work in such situation.

conf.getClassByName(conf.get(DBConfiguration.DRIVER_CLASS_PROPERTY));

Is there any similar issue? Sorry that I can not find any JIRA about this problem.

--
Thanks,
Shixiong Zhu



--
Regards
Vasanth kumar RJ